For at least a century and a half attempts have been made to explain the origin of medieval portolan charts but no sustainable answer has been found. In the absence of solid documentary evidence, clues, deduction, analogy and intuition have had to be used instead. The revisionist conclusions that follow are the result of a lengthy analysis.
Portolan charts are characterised by unprecedented geometric precision and newly invented conventions, among which are an underlying mesh of direction lines, place-names restricted to the coast, empty seas, intentional generalisation of the coastline, and coded markings for navigational dangers. Furthermore, the very concept of a chart for marine navigation was itself new. The area covered by the oldest surviving marine chart, the Carte Pisane (c.1270), namely the Mediterranean, Black Sea and sections of the Atlantic coasts, would remain the norm for the next two centuries.
Before the appearance of the portolan chart an open-sea (pelagic) mariner, from any early period, would have needed a mental map of at least part of the Mediterranean, allied to the ability (prior to the invention of the magnetic needle) to determine direction, by means of a mental wind compass – for which there is indeed documentation. He would not have set out to sea otherwise. The mental maps would have been formed out of an expanding network of individual courses, memorised during a pilot’s life. Since many voyages would have involved ports around the sea’s periphery those, collectively, could have served to define the Mediterranean’s limits. Based on a collaborative pooling of those mental maps it would have been possible to ‘download’ the whole network as a single graphic design. Once the Mediterranean was visible as a whole, the conflicting estimates of a place’s position could be reconciled and omissions rectified.
Circumstantial evidence places the birth of the portolan chart in an unidentified west-coast Italian port, between 1154 and 1204. It was clearly designed by and for pelagic sailors and there is no evidence of institutional involvement or external financing. As an object of commerce, the charts had to be worth more to the sailor more than the cost of their hand-production. Since most of the charts’ users would have been illiterate, they carry no instructions for use, which had to be supplied orally instead.
No mathematical calculations or measurements were involved. In essence, the portolan chart was not a geographic or cartographic construct but a memorised experience transposed into a geometrically consistent graphic form, with the coastal outlines and toponymy added afterwards.
The essay starts with a summary critique of previous explanations for the origin of the portolan chart. None had managed to provide a comprehensive answer or one that is historically plausible, which helps explain why none has proved generally persuasive. Rather than devoting much time to their limitations – although their arguments are challenged at the appropriate points – it seems more profitable to set out instead what it is hoped is a feasible alternative thesis. Inevitably, it must remain scientifically unproven and partly speculative, but it does incorporate what little hard evidence there is, and tries to match that with the (sketchy) understanding of early navigational practices, married to what is known of human needs and motivation.
A forceful argument will be made in support of the statement that there are no identified antecedents for the portolan charts. In particular, it is shown that Muhammad al-Idrīsī’s Charta Rogeriana of 1154 could have played no part in the origins story, whether as model or imitation [Powerpoint, Slide 1]. 1 Instead, the range of unique innovations seen in portolan charts (which, significantly, continue throughout the early period) makes it almost impossible that they could have had any predecessor.
The essay then states its central claim: that the charts must have derived, in some fashion, from the collective navigational memory of Mediterranean mariners. Open-sea sailing – as distinct from voyages that hugged an always-visible coastline – had as its first requirement that the pilot and helmsman knew where they were heading, before they left port. Proceeding without that knowledge would be more than foolhardy, verging on suicidal. That is at the heart of this thesis. The one-sentence foundation for this theory can be summarised thus: medieval pilots must have had a clear idea of the route to their destination, coupled with a reliable inbuilt mental wind compass that could envision the required bearing at all times.
Historians naturally seek out and value textual records. In this instance, the oldest surviving chart (the Carte PisaneAccepted as the oldest surviving portolan chart, c.1270, its author and place of origin are unknown. It has been in the Bibliothèque nationale de France since 1839 (Cartes et Plans, B 1118)) was certainly preceded by one pilot book (the Liber de existencia riveriarum et forma maris nostri Mediterranei – on which see a brief description in section E.1a), with a second (Lo compasso de navegare – for details of which see E.1b) being perhaps its approximate contemporary. The inter-relationship (if there is any) of those three unique, unsigned documents – none clearly datable – continues to be much discussed in the context of the ‘chicken and egg’ question of their respective priority. The charts’ supposed period of origin (now that the best estimate points to the late 12th century) is likely to have roughly coincided with the first appearance of a magnetic compass. Again, the historical record is unclear but an attempt is made to assess what significance (if any) the introduction of that navigational aid might have had for the genesis of the portolan chart. What would, however, have been of central importance was the wind compass held in a pilot’s memory. The discovery that the structure of this vital aid was neither described by contemporaries (apparently) nor had been analysed in any detail by previous historians, led to a lengthy digression co-authored with Roel Nicolai (see The mental wind compass of the medieval Mediterranean: the rediscovery of its structure and interpretations of its use, which has already been published separately).
The topics covered in this essay are listed in a separate hyperlinked MENU. Part 1 will delve into the charts’ prehistory to try to piece together the likely developmental stages that preceded the oldest survivor. 2 Spatial cognition, and mental maps in general, will be considered, along with medieval navigation and the charts’ possible (but here discounted) antecedents. Part 2 elaborates on the hypothetical ‘downloading’ of the mental map of the Mediterranean, while discussing, inter alia, the charts’ main features and purposes.
Recent (but pre-electronic) marine charts display almost all that a navigator needs, when used in conjunction with a pilot guide. The medieval chart, on the other hand, seems to have stood alone without secondary support. Or to be more exact, the essential elucidation must have come from sources little-discussed by historians, namely orally-transmitted instructions and the memorised experience of previous voyages. Orality and memory have a much larger place in portolan-chart history than literacy. Not only will it be argued here that the charts had no textual antecedent at all, but also that the portolani (Singular ‘portolano’ and more usually called ‘portolans’ – which can be confused with the charts) these were medieval guides to the coastal places around the Mediterranean, listing the distances between them. They also include open-sea (pelagic) routes, which had in the past been proposed as a possible source for the chart, must now be interpreted as depending on pelagic information from a marine chart for their very existence.
The essay is rounded off with a brief look at 16th-century surveys outside the Mediterranean, seeking any analogies that could have relevance for the prehistory of the portolan chart, followed by concluding remarks. An account of the essay’s methodology, summary conclusions and possibilities for future research are set out in separate webpages.
Constant reference is made to the following documents:
“Among the research problems connected with the portolan charts, the question of their origin is perhaps the most intractable”. 5 Published almost thirty-five years ago, that statement still applies. Winston Churchill’s description of Russia’s intentions in 1939 as “a riddle, wrapped in a mystery, inside an enigma; but perhaps there is a key”, matches the present difficulty. It is hoped that Churchill’s optimistic coda will now prove to be equally apt in this case. Was the origin of the portolan chart hiding in plain sight all along?
The assertion underlying this thesis, namely that a mental chart of the Mediterranean, paired with a relatively precise mental wind compass, must have been in existence, in some form, for millennia and that the portolan chart could be understood only as a collaborative downloading of that information, was considered outrageously revolutionary at its first airing in 2016. While it is yet to receive unqualified backing, resistance seems to be weakening.
But, at the risk of lessening the impact of this essay, it has to be pointed out that most of the argument’s individual propositions had already been asserted by previous historians, as evidenced by a number of the quotations in what follows. The novelty – because some of that can fairly be claimed – must lie in the fact that here, for the first time, those disparate claims and suggestions have been moulded into a single, and it is hoped, coherent theory.
For at least a century and a half, historians have struggled to reconcile the realistic outlines of portolan charts with their medieval context, since it was the first map covering a large area to be defined by its overall realism. The question usually asked was how that level of geometric precision could have been achieved with medieval instruments or mathematical expertise, and, above all, with the mind-set of the time? To suggest, as this essay does, the outlines of a possible solution may seem bold if not downright foolhardy. However, since nothing has plausibly replaced those earlier theories (now generally dismissed) which focused on a Classical or Islamic origin, or even a very ancient creation, the challenge needs to be faced. 6
There is no certain ‘history’ of the portolan charts prior to the earliest survivor, the Carte PisaneAccepted as the oldest surviving portolan chart, c.1270, its author and place of origin are unknown. It has been in the Bibliothèque nationale de France since 1839 (Cartes et Plans, B 1118) , which, as was confirmed in 2016, and later by carbon testing, should be dated about 1270. For scans of the chart as it now is, and an 1852 facsimile made prior to the damage it suffered, see [Powerpoint, Slides 2 & 3, showing respectively the original and facsimile versions]. Prior to that is a prehistory almost as empty as the open sea, or with occasional half-seen features looming through the mist. Nobody recorded the charts’ birth. Neither the charts themselves nor any extant text throw direct light on their genesis or antecedents. Instead we have to rely on scattered written fragments: among those are passing references in later official records (usually emphasising their necessity at sea, without detailing how they were used), or comments about marketing matters, wills and legal disputes. 7 But nothing is said about their origin, purpose, on-board role, or the method used to reproduce the charts faithfully. If any pilgrim or crusader with an enquiring mind had sought information on those topics from a crew member, and then recorded it in their memorandum book, no trace of that has been found. The earliest landsmen’s descriptions of sailors consulting their charts date from the 15th century. 8
This leaves the charts as crucial witnesses to their own history. Most of what is reliably known about them derives from close analytical study of the oldest survivors, and particularly their toponymy.
In the absence of archival sources to provide part of the answers, a possible hypothesis will be outlined, echoing what Ramon Pujades expressed in his monumental survey of 2007, namely that "a historical solution must be sought to what others have tended to treat as a purely geographical-cartographical problem". 9
There are five interconnected questions needing to be addressed: when, where, by whom, how and why were the earliest portolan charts constructed? Cartometric analysis can certainly help with the technical component of the 'how' aspect, and explaining how the outlines made their way onto a map demands a joint historical and numerical answer, for which the results of cartometric analyses must be carefully considered. But the four other outstanding origin questions (when, where, by whom and why) are unlikely to be revealed through mathematics.
Instead, if there is any chance of determining where the portolan chart came from we must try to envisage the world out of which it emerged, the environment in which its creators and first users moved. The scant historical evidence must be sought out, both textual and cartographic, and when that runs out, we have to fall back on the constant verities of human nature and need, set into the specific context of medieval Mediterranean navigation. Ultimately, hypothesis, logic, common sense, intuition, analogy – none of which match the requirements usually demanded of historical evidence – will have to play an important role.
One aspect that must be squarely faced is the navigational capability of the medieval sailor. In a doctoral dissertation of 2014, Roel Nicolai concluded, at the end of a detailed cartometric investigation, that medieval mariners would not have had sufficient ability or equipment to have achieved the positional accuracy of the portolan charts: "The geodetic basis of the charts, expressed in their accuracy and their map projection, is far beyond the capabilities of the European Middle Ages". 10 That left him with the unanswered (and probably unanswerable) question: which era and place could have been responsible?
It appears to be the most likely scenario that Italian merchants acquired a body of ancient maps or charts through their trade with Constantinople ... The merit of the Italian mariner-traders would have been that they saw the potential of these maps, while the Byzantines, who preserved the heritage of antiquity but did nothing with it, may not have been greatly interested in them. It will have to be borne in mind that no person in the Middle Ages could have known how accurate these maps were. 11
This essay calls for historical empathy, taking a more generous view of medieval aptitude and ingenuity, working on the assumption that people will always develop the skills they need for survival. It also argues that the experience of Mediterranean navigators would have been sufficient to supply the basis for the charts’ outlines, and that the generally accepted west coast of Italy should be retained as their place of origin, probably in the late 12th century. In other words, the central issue being proposed is not whether the early mariners had the geometrical ability to make a chart, but rather whether the level of their navigational skills, including direction-finding – which must have been commonplace among them for centuries – would have been sufficient for that purpose.
Prior to the emergence of the portolan chart, all navigational knowledge must have been memorised and shared orally. Hence the central task for any origins theory is to find a plausible way of explaining how the Mediterranean outlines made their way onto a chart in the first place. Significant research by Joaquim Alves Gaspar in 2019 has allowed us to reinterpret an important section of the oldest textual reference known, the LiberThe ’Liber de existencia riveriarum’, c.1210, written in Latin, is the oldest surviving guide to the Mediterranean, giving the distance and direction between places along the coast and across the open sea (Cotton MS Domitian A XIII, ff. 114r–129v). 12 Its statements of the distance and direction between paired places on the mainland coasts or islands, were previously considered to describe actual open-sea (pelagic) voyages. However, some were impossible, since they cross land, and that interpretation is no longer generally accepted. Instead – and this is the crucial point – it has become clear that the source for those statements was not direct sailed experience but rather measurements taken selectively from some kind of cartographic document. This confirmed that the portolan chart (or its antecedent) pre-dated the Liber, thus moving the focus away from a textual source towards an oral and graphic one.
Even more important, Gaspar was able to show that when the positions of all the paired termini at either end of those Liber statements were plotted out, a geometric diagram was created which defined the outlines of the entire Mediterranean with approximate accuracy. It is this (necessarily hypothetical) diagram – the result of what is here being termed ’inadvertent triangulation’An invented term for the hypothetical process by which pilots, before there was a marine chart, could have built up a mental network of the interrelationships between Mediterranean headlands, by means of observed directions and estimated distances. No mathematical calculations would have been involved – that, it is proposed, was the portolan chart’s source. So, the first question that has to be convincingly answered is this: what was the source of the pelagic information which would have been sufficient to build a wholly new cartographic image?
There are two other important linked questions that demand answers. First, given that their relatively small scale provided insufficient detail for the purposes of precise navigation, why were the charts conceived and created in the first place, and, second, why were they replicated for the use of paying customers for four centuries thereafter?
The ornamented charts that survive in disproportionate numbers from later periods were evidently not intended for use at sea. But if, as is still occasionally claimed, even unillustrated portolan charts served no navigational function either, then far more would have survived, instead of being worn out from overuse in inhospitable conditions. Furthermore, it is only once it is assumed the charts had a practical seafaring purpose that their peculiarities make sense.
While this essay is firmly focused on the charts’ hypothetical origins, it also seeks out evidence and meaning from the earliest documented periods, and especially from close examination of the oldest surviving charts themselves. Circumstantial evidence and the application of contextual logic offer a better chance of building up a picture, however tentative, of what the lost prototype chart might have looked like. There are some indications available, however, even if only by analogy. The Carte PisaneAccepted as the oldest surviving portolan chart, c.1270, its author and place of origin are unknown. It has been in the Bibliothèque nationale de France since 1839 (Cartes et Plans, B 1118) and its distant descendants as late as 1700 share a cartographic language made up of so many common features, as well as consistent purposes, that there a strong argument for tentatively extrapolating those backwards into the charts’ prehistory.
New logical deduction allows the date of the portolan chart’s inception to be narrowed to a brief window. As is explained in more detail below, 13 no marine chart could have been circulating before 1154, because the fifteen years al-Idrīsī spent gathering data for his vast world map of that year the (Charta RogerianaA 3.5 metre wall-map of the world created, in Arabic, by Muhammad al-Idrīsī in Palermo, Sicily for the Norman king Roger II in 1154, and preserved, in the form of 70 sections, in several copies of a manuscript text) would certainly have included elements from a portolan chart if he had seen one. Based in Sicily, at the centre of the Mediterranean, it would have been impossible to avoid them. Conversely, working from the other direction, the new understanding that the Liber’s author was evidently using a marine chart for his pelagic measurements means that a functioning antecedent chart must have already been in place by the time that was written. The Liber’s sketchy details for the Black Sea (not taken from a chart) would fit in with a date after, but only shortly after, access was opened up to that in 1204. On the strength of those observations, the newly proposed date for the Liber is c.1210, and for the chart it was copying from, lacking the Black Sea, earlier than 1204.
In terms of the charts’ overall coverage, therefore, four phases can be distinguished: first, the core region, the Mediterranean, devised probably between 1154 and 1200; second, the eastwards extension to take in the Black Sea during the 13th century; third, the addition of the Atlantic coasts probably in the period 1300-1330; and then the steady recording of successive Portuguese exploratory voyages down the west coast of Africa in the 15th, leading to the voyages of discovery in the 16th.
There are intriguing parallels between the study of portolan chart origins and archaeology. What emerges from the soil might be the precise and complete outline of a building. Its purpose, say as a place of worship, might be broadly inferred from analogy with others elsewhere (if such existed). But who used it, what they believed, and what form their rituals took would probably remain elusive. In the Carte Pisane Accepted as the oldest surviving portolan chart, c.1270, its author and place of origin are unknown. It has been in the Bibliothèque nationale de France since 1839 (Cartes et Plans, B 1118) we have the equivalent of that ancient building but little or no direct evidence as to how or why it was made. It did not come with a manual. With a leap of imagination, it might be possible to see the charts’ toponyms as akin to the archaeologists’ postholes, outlining a definite feature but requiring other evidence to establish their purpose – or in this case why those place-names were chosen.
The portolan chart is truly a cartographic masterpiece. The unprecedented step of setting down on parchment a precise maritime chart is comparable to replacing a quill-pen with a computer. The wide range of its cartographic conventions, almost none of which had been seen before, will be discussed individually. The word ‘invention’ seems appropriate, given that a number of the aspects of the chart’s cartographic language could, in a modern age, have been patented. It is easy to see cartographic innovations as unexceptional when they appear to be so sensible, and apparently timeless. But somebody had to have that ‘obvious’ idea, and then it had to be imitated. That the techniques introduced on portolan charts continued for so long is testimony to the clear and imaginative thinking of the unknown mariners who devised them.
They are the first maps of the Mediterranean and Black Sea that are fully recognisable to us, and what they offered seamen was unparalleled in its complexity and practical usefulness compared to anything made for landsmen. While merely a helpful guide for voyages that hugged the coast, the charts would speedily have become an indispensable aid for navigation when out at sea, where no land was in view to provide orientation. For an experienced pilot it would fill out the parts he did not already know, while a non-sailor would have gained access for the first time to the maps that mariners had always held in their heads.
Before starting to grapple with the origin question itself, we need to try and envisage the thinking and experience of medieval Mediterranean sailors prior to the portolan chart. It must first be understood that they were unlikely to have seen any cartographic image of their sea, and certainly not one that could have been of navigational relevance. Indeed, it can probably be assumed that mariners of the time had no clear concept of a drawn ‘map‘ of any kind. In devising a pragmatic working tool, the chart’s creators would have had to start from first principles. Their approach would have been free of ideology, imposed rules or precedent. What features were included and how they were treated depended on one thing only: how relevant they were for the charts’ purposes. That the cartographic conventions used on the oldest surviving chart cannot be found on any extant work from that time or earlier, is solid evidence that the portolan charts are sui generis. Their largest single innovation is undoubtedly an idea: the concept of the portolan chart, added to that the realisation that an animal skin, untrimmed, could be used to carry a map of the Mediterranean. In other words, what is special about the charts is their imaginative uniqueness. They were revolutionary not evolutionary. Paul Souriau’s verdict was that “Invention is not creation ‘out-of-the-blue’, but rather a combination of pre-existing ideas”. 14 There is little evidence of that in the case of the portolan charts even if they did emerge out of the deep blue sea.
Medieval navigators shared (broadly) the way they named places, how they described direction and how they measured distances – in ways that would be lost in later years and which we now struggle to replicate. Was it not logical that having already freely exchanged the details of pelagic courses and the mysteries of their wind compass they should pool their knowledge in a shared marine chart? After all, unlike other artisans, they were not in competition with one another; on the contrary, they were bonded by the common problems and threats they faced.
To put the achievements into context, the canvas under consideration concerns the world’s largest inland sea, the Mediterranean – with a width of 3,800 km and a north-south extent of 1,100 km, involving an overall coastline of some 22,000 km. To that should be added the 4,300 km coastal extent of the Black Sea, without considering those sections of the Atlantic coasts that were included on the standard chart.
This extended essay attempts to solve what may be the longest-lasting mystery in the history of cartography. 15 The conclusions it reaches run counter to existing theories that the charts’ source was text-based: whether some record of individual pelagic courses, or the littoral toponymic progression documented in the portolani(Singular ‘portolano’ and more usually called ‘portolans’ – which can be confused with the charts) these were medieval guides to the coastal places around the Mediterranean, listing the distances between them. They also include open-sea (pelagic) routes. Instead it will be argued, from the best indications available, that the origin should be identified in the joined-up network formed of the termini of those open-sea (pelagic) courses, which had been held from time immemorial in the memories of Mediterranean sailors.
There is an essential distinction that whereas the land divides (whether by language, culture, politics or topography) the sea unites. In medieval times, on terra firma, outside Latin-using circles, there was a babel of languages. Similarly, units of linear measurement had proliferated, even when they were notionally based on parts of the human body. Measurement would not come to be widely standardised until the metre was devised in Revolutionary France. At sea, on the other hand, such disparities were negated by a unifying environment made up of water (only very loosely divisible), the islands dropped into it, and the abutting coastlines.
In ‘Men of Sea. The making of an Identity’ one passage defines what sets sailors apart from others [note the timeless comment in the final sentence]:
The identity of the ancient sailors or men of sea according to our research is based on an open opposition to earth-based society and it is recognizable through the extremely dangerous conditions of their work and their isolation, their particular customs and their deep religiosity and superstitious attitudes, obviously encouraged because of the evident risks of their activities. These basic features were basically shared for every sailor from Antiquity onwards. 16
Life at sea did not just benefit from co-operation it must have largely depended upon it. Leaving aside declared enemies, it would be surprising if those involved in maritime trade had not developed a tradition of mutual assistance. Even if there was commercial rivalry, that would have taken second place to the sharing of information about optimal routes, navigational dangers, the presence of pirates, any nearby ship afflicted with plague, local weather conditions, and so on. They were, after all, engaged in an endless struggle in the face of shared difficulties and risks. In that, contradictory sense, "If land is cosmos, ordered, the sea or the ocean is chaos, unordered". 17 Why would long-distance pilots have held back potentially life-saving information from those who might in time reciprocate? 18
So, where social cohesion on terra firma had to contend with various fissiparous tendencies, the marine experience was very different. The Mediterranean was a shared sea and sailors were able to travel, in principle, to any part of it without hindrance. Its ports, along with the ships’ crews, housed a shifting population that was probably more heterogeneous than could be found anywhere else. Agreeing on a single unit to measure distance, sometimes across the featureless sea, must have been a precondition for the piloting of merchant vessels in the open sea. Hence the adoption of a ‘portolan mile’, even if those who used it seem not to have realised that there were regional differences in the way it was interpreted. 19 Seamen also needed to agree on consistency in the naming of places and natural features, as well as an understanding of the subdivisions in their shared wind compass. 20
Besides those bedrocks of maritime lore there was a common cartographic language for the symbols on portolan charts that highlighted hazards and (admittedly, a slightly later development) the intentionally unrealistic shapes given to the islands in the Aegean and elsewhere as a mnemonic aid. When the location of the prime meridian at Greenwich was finally decided in 1884, replacing numerous nationally preferred alternatives, that was no more than an acknowledgement of the fact that most mariners were already using Greenwich, paralleling that same tendency towards maritime conformity that can be seen in the medieval period.
It is remarkable that, during a period of at least 150 years, there has been no plausible explanation as to precisely how the information shown on the portolan charts was first gathered and subsequently processed. Roel Nicolai’s impressively thorough doctoral thesis was forced into a negative conclusion: “The geodetic and cartographic origin of portolan charts does not lie in medieval Europe”, but he was unable to offer an alternative birthplace. 21 The explanation, and there has to be a rational one, cannot depend on some unidentified earlier civilisation.
No contemporary text has described the data-gathering process that led to the creation of the portolan chart, indeed it seems highly improbable that such an account would ever have been written. Hence the only primary, albeit indirect, sources at our disposal are the earliest surviving charts (from the latter 13th century onwards), and two portolani (Singular ‘portolano’ and more usually called ‘portolans’ – which can be confused with the charts) these were medieval guides to the coastal places around the Mediterranean, listing the distances between them. They also include open-sea (pelagic) routes apparently from that same century.
The central question that has first to be decided is this:
Were the charts created out of a coastal survey, by stitching together regional surveys, or by joining up into a single system the open-sea (‘pelagic’) courses across the Mediterranean?
There seem to be four possible hypotheses:
(A) Joining up the statements in a portolano
Jonathan Lanman’s 1987 essay 22 purported to demonstrate that an overall chart could have been derived by plotting onto a map the stated directions and distances from one port to the next all the way round the Mediterranean (with its islands) and the Black Sea, as is described in Lo compasso’Lo compasso de navegare’, c.1260-96, written in Italian and apparently designed for sailors, is much more detailed than the earlier ’Liber’ (Staatsbibliothek, Berlin, MS Hamilton 396).
That must fail for one simple reason. While plausible outlines might be arrived at by those means for short stretches of coastline, the inevitable imprecision of both the stated distances (in miglia = miles) and the ‘wind compass’ directions would have made it impossible to build a total map of the Mediterranean in that way. 23
Taking into account expected textual error and omissions in the sources used, this would have introduced steadily growing distortion into the broader picture. Such a method, carried out in sections, would never have reproduced the overall geometry of the Mediterranean in any usable form. There could have been no accurate matching of the north and south coasts, no reliable pairing of Spain’s features, for example with those of the Levant, and no understanding of the correct proportions of the Black Sea. As Joaquim Alves Gaspar concluded: “However recognizable in general terms the resultant outlines of the Mediterranean Sea, their accuracy and detail are hardly comparable with those of the charts they were intended to replicate”. 24
(B) A coastal survey
The second hypothesis would be a putative coastal survey of both the entire littoral of the Mediterranean (as already mentioned, the world’s largest inland sea) and the Black Sea, including the former’s islands, presumably in a manner comparable in some way to those carried out elsewhere in later centuries.
This would be an elaboration of (A). Apart from repeating the problem of overall consistency, this can be readily dismissed on a number of other grounds. The most obvious is that it is unforgivably anachronistic to suggest that anybody in the 12th or 13th centuries would have contemplated sailing around the Mediterranean purely to create a general chart – of a kind never previously envisaged. Not only is there no precedent for any expedition tasked solely with producing an accurate survey of a coastline before, at the earliest, the 16th century, but it would have been well beyond the technical capabilities of the Middle Ages. Furthermore, it is impossible to envisage anybody conceiving, and paying, for such a venture. Indeed, later surveys were a side-product of voyages seeking to discover lands that might provide raw materials, trading opportunities or simply new territory. Since the coasts covered by the portolan chart must have already been adequately understood in general terms by sailors, the Mediterranean provided none of those incentives.
The scale of such an operation meant that it would probably have taken several years, and involved a ship with a dedicated crew. There would need to have been at least one attendant boat for close in-shore work as well – for instance in the Dalmatian islands and the Aegean – or for coasts that were bordered by shallows.
Finally, given its predictable inaccuracy, what would have been the purpose of such an exercise? How would it have been possible to identify and remove any errors inevitably produced by such a hypothetical coastal survey? The only logical way to achieve that would have been through the input of the combined pelagic courses (to be explained later). And why would developments have occurred in that sequence, given that the charts’ main purpose seems logically to have been to provide a tool for long-distance sailors, for whom an uncorrected coastal survey would have been of little or no use.
It is true that no one, to my knowledge, has directly suggested such a systematic coastal survey but it seems to be generally assumed (other than by Roel Nicolai and proponents of an Islamic origin), 25 that the portolan charts’ information is entirely medieval. It is just that nobody has been able to suggest how that might have been gathered and brought together in the form of a marine chart.
(C) The sub-charts theory
The contention that the portolan chart emerged from the joining up of a series of sub-charts of the basins and zones of the Mediterranean, which seems to be increasingly accepted, is discussed in detail later – and there critiqued in detail. 26
(D) Mental maps
The fourth solution proposed for the enduring enigma of portolan chart origin is the source identified in this essay, namely the spatial memory of countless longer voyages that must have been held in the head of every widely-travelled sailor, and which, at some point, was set down in graphic form.
Of one thing we can be sure: whether the creation of the portolan charts came about by means of a coastal survey or by the drawing out of memorised courses, the work must have been carried out on board ship, and the methods must have been consistent with medieval shipboard practices and skills. Thus the focus on the charts’ creators must be paired with equal consideration for the ships involved [Powerpoint, Slide 4]. The charts represent a seaman’s view, and to hope to understand the process of creation we have to place ourselves mentally on the rolling deck of a ship.
THE ENVIRONMENT OUT OF WHICH THE PORTOLAN CHART MATERIALISED
Any search for plausible antecedents of the portolan chart needs to ask which of the cartographic models known to have been extant [though not necessarily accessible] at the end of the 12th century might have played a part. In what ways would different cartographic types, exemplified for example by the mappaemundi'World maps' in Latin (singular, mappamundi). Used to distinguish medieval maps of the world from those of Ptolemy and the portolan charts, the Peutinger Table, Matthew Paris’s itinerary maps, the Charta Rogeriana 27 or regional maps and diagrams, have helped provide any kind of realistic picture of the Mediterranean and Black seas? 28 [Powerpoint, Slides 1 & 5]. Furthermore, who, in 1200, would have needed, or been able to make use of, a realistic outline of the known world, with positional geometry as its primary concern?
Ptolemy’s astronomically determined co-ordinate geography might seem to be a suitable candidate (even assuming that it was available in Western Europe at that time via Islamic intermediaries, which is unlikely). The Geographia’s coordinates set out what was known in Alexandria in the second century CE and would not start to be updated until the Renaissance. In the period when the portolan chart seems to have emerged, cartographers had other priorities besides Euclidian accuracy. Indeed, despite the example of the portolan charts, with a few exceptions a regional cartography that used a measured scale and concentrated on the correct relative positioning of places – what might be termed ‘proto-scientific’ – is not seen for several centuries.
We should not have to rely on hypothetical antecedent maps, which are not only physically lost but also absent from the written record. If it is felt that such must have existed, how is it envisaged they were created and who would have drawn or used them? Those who support the claims of non-mariners as the charts’ progenitors need to identify who else, realistically, could have been involved. It is much more likely that the nascent portolan chart was ‘hidden in plain sight’ in mariners’ memories than that an invaluable Roman device was lost for 1000 years. Even if Greek mathematicians or Roman surveyors had turned their minds to the question of a marine chart, where would they have obtained the necessary information? Their periploi provide even less information than the medieval successors to those, the portolani (Singular ‘portolano’ and more usually called ‘portolans’ – which can be confused with the charts) these were medieval guides to the coastal places around the Mediterranean, listing the distances between them. They also include open-sea (pelagic) routes. Furthermore, the identical source question posed about the medieval charts would have to be asked in the case of a hypothetical Classical origin.
The iterative argument, which assumes that portolan charts must represent a continuation of one or more preceding cartographic genres, is not only contradicted by the lack of any such models but, even more compellingly, by the charts’ inclusion of a suite of unprecedented conventions, probably, in both number and originality, without parallel in the history of cartography. 29
It cannot be said for certain that the portolan charts’ creator(s) had never seen a map of any kind. 30 However, we can be sure that whoever drew the Carte PisaneAccepted as the oldest surviving portolan chart, c.1270, its author and place of origin are unknown. It has been in the Bibliothèque nationale de France since 1839 (Cartes et Plans, B 1118) was unaware of any map attempting to cover seriously those sections of the North Atlantic coasts which he casually included: whether Ptolemy, the descendants of a Roman model typified by the Anglo-Saxon (or Cotton) map,31 or al-Idrīsī’s Charta RogerianaA 3.5 metre wall- map of the world created, in Arabic, by Muhammad al-Idrīsī in Palermo, Sicily for the Norman king Roger II in 1154, and preserved, in the form of 70 sections, in several copies of a manuscript text. 32 The most logical explanation for that new cartographic language lies in the portolan charts’ clear focus on navigation – to the extent that almost everything else is omitted – confirming that they were created, de novo, for the use of navigators.
Assertion: Most sailors around 1200 were illiterate so why would a textual origin for the charts be likely?
Possibly because historians are used to dealing primarily with textual evidence, there seems to be a tendency – even perhaps an assumption – that, if the origin of portolan charts is ever discovered, it will take a written form, or at least have emerged from a literate group. Ramon Pujades articulated that viewpoint clearly, as in the following examples:
They were the products of the written culture of a specific period
The chronology of the advent and dissemination of nautical charts is totally inseparable from that of the rise of vernacular Romance languages to the category of vehicles of written expression
The information the [Liber’s] author had compiled to write his portolan and draw his mappamundi came from data on distances and directions amassed by a number of seamen-merchants-military men from the second half of the twelfth century who had recently learnt to read and write 33
Likewise, Patrick Gautier Dalché suggested that a pilot book which pre-dated the LiberThe ’Liber de existencia riveriarum’, c.1210, written in Latin, is the oldest surviving guide to the Mediterranean, giving the distance and direction between places along the coast and across the open sea (Cotton MS Domitian A XIII, ff. 114r–129v) would have been at least a partial source for the charts. 34 The most likely textual source had at first appeared to be the Liber. However, recent re-interpretation of its pelagic statements 35 has concluded, first, that those do not describe actual open-sea courses and, second, that the information they contained could only have come to the Liber’s author from a lost cartographic drawing, from which he had extracted those measurements. Thus the earliest relevant surviving text proves not only to have played no part in the charts’ invention, but also to post-date what must have been some kind of graphic antecedent to the portolan chart.
Besides there being no surviving textual source, there are no references to missing works of that nature either. Even if a supposedly relevant text was identified it would do no more than prompt a further question: what, in turn, was its source? It would be like the rainbow, not the crock of gold at its foot. Furthermore, it is argued here that there is no logical reason to suppose that there would have been any textual stage at all in the charts’ origin and early development. 36 Instead, a diagram of open-sea courses based on sailors’ shared memories is posited as the underlying element, with coastlines and toponyms provided separately afterwards.
The portolan chart is a graphic document with a quasi-mathematical underpinning. No sign of a literary element has yet been identified in the charts’ DNA. That is surely no more than would be expected when the navigators’ milieu is taken into account. Sailors would probably have met, not in the study of a savant, let alone a monastic scriptorium, but on board a ship or in a quayside drinking establishment. Why is it logical to expect that a mental ‘map’ should have been downloaded into text before being re-envisioned in a graphic form which mirrored the original information? As the commentators on the 11th-century Islamic Book of Curiosities point out: “a transition from text to map is not as intuitive as it may seem to us today”. 37
This chimaera of a missing urtext out of which the portolan chart emerged must be unmasked as an unfounded assumption (perhaps wish?) for the charts to have a documentary rather than mixed graphic and oral origin. 38 The textual-origin argument ignores the evidence that much of the crucial information on the portolan charts could have come only from memorised experience. Nor could the charts’ navigational detail (for example the coded dangers) have been reproduced adequately in a text.
Hence, not only is there no indication that a textual source ever existed, neither is there any likelihood of that having happened.
The comments above relate to the hypothetical textual antecedents for the portolan chart. For a discussion of text compared to orality and memory, in the context of the written portolani and navigational practice, see L.3. ‘Literacy or illiteracy’.
From an overview of early Islamic navigation, carried out by Yossef Rapoport and Emilie Savage-Smith, in connection with the 11th-century Book of Curiosities [Powerpoint, Slide 6], it has been established that there was plentiful, detailed information available to Arabic speakers and readers. 39 Indeed, the book’s “recording of navigation data in a systematic way is unique and distinctive”. 40 The portolan chart, despite its great originality, must defer in one overall respect to that Arabic manuscript, which has been justly described as the “first surviving example of a map looking at the coasts from the sea”. 41 However, realistic coastal outlines were intentionally excluded from the maps in The Book of Curiosities. What is notable is the mis-match between the text and the accompanying graphic representations, which were abstract and generalised. Indeed the work’s author explains that his marine maps were not intended to be “accurate representations”. 42
It is valid to ask why the Islamic world did not invent the portolan chart, given that in the Mediterranean, “a shared and contested space, the problems facing Muslim and Christian navigators were the same. Much of the maritime nomenclature was common across the boundaries of faith, and the technologies that Christian and Muslim mariners used were broadly similar”. 43 Despite this, Rapoport and Savage-Smith rebut past claims to that effect: “In view of the evidence of the maritime maps of The Book of Curiosities, it seems highly unlikely that some early version of portolan maps was known in Fatimid Egypt. This is worth emphasizing because some have argued that portolan maps first emerged in the Islamic world”. 44
That Italy rather than the eastern Mediterranean was the birthplace of the portolan chart might have been no more than accident. But it should not be assumed, from the overlapping navigational needs, that there were no major differences. One of the largest was the omission in The Book of Curiosities of references to hazards faced by shipping, yet that was certainly one of the main purposes of the portolan chart. Furthermore, the Islamic text’s concentration on bays, 45 which presumably shows a concern for ports with their mercantile relevance, contrasts with the portolan charts’ focus on the feature of the greatest concern for navigators, namely headlands. 46
The map under consideration was produced in 1154 or a little later, by Muhammad al-Idrīsī, for Roger II, king of Sicily. It has come down to us in the form of seventy separated sections, which, if they had been joined up, would have had the proportion of a 3.5 metre-wide wall map. That masterpiece needs to be clearly distinguished from a much-reproduced small circular world map, whose connection to al-Idrīsī is tenuous and whose importance has been overstated.
The large map, which is here referred to as the Charta Rogeriana, is dispersed through the pages of a manuscript volume, Nuzhat al-mushtāq [The book of pleasant journeys into faraway lands]. At issue is the question of whether the Charta incorporates any of the conventions otherwise specific to the portolan chart. If that was the case it would indicate that the latter was in existence prior to 1154. Alternatively, since the Charta is the only surviving map from the period before 1200 that could conceivably have provided inspiration for the portolan chart’s creators, is there any evidence that they had borrowed from the Charta? 47 In other words, which came first, and was either influenced by the other?
The attempt to answer that apparently simple question ran up against the problem that many of the details of the Charta’s creation and its later dissemination had to be teased out from conflicting and contradictory evidence. That analysis can be read in greater detail in a recently published web article. 48 The main conclusions that confirm the lack of mutual influence between the Charta and the portolan chart are set out in the following sections, which contrast the content and purpose of each.
A.3b.1. Comparison between the content of the Charta and the portolan charts
The Charta’s place-names are at their densest around the coasts – which would fit in with Roger’s desire to know about 'seas and gulfs' – but they appear to refer to settlements only, not to natural features, though a few rivers and mountain ranges are identified. However, despite the Charta’s deserved reputation for innovation and thoroughness, it would have been of limited use to a sailor. It is true that what is considered one of the signature features of the portolan charts, namely the placement of the toponyms inside the coastline, is also found on the Charta, but there is a significant difference. Whereas the portolan chart’s toponymy winds its way round the coastline in an unbroken sequence, with the names placed at right angles to that – which meant that the user had to rotate the chart to see them the right way up – the Charta’s toponyms are generally placed horizontally, to be read from a single viewpoint like normal text. Furthermore, the Charta’s patterned sea indicates there was no intention of depicting any offshore dangers, which was one of the portolan charts’ primary functions. Not even the feared Skerki Bank, to the west of Sicily – and hence not far from Palermo, where the Charta was drawn – was included. 49
Interestingly, Sicily’s fairly regular shape was conveyed realistically, even if its size was massively enlarged. Although at first glance that would appear to flatter al-Idrīsī’s royal patron specifically, some of the other islands are also re-sized, whether magnified or reduced. For example, while Sicily is shown as about four times the size of Sardinia, that, in turn, is three-times larger than Corsica. This is another indication that geographical truth was not al-Idrīsī’s only consideration. By contrast, although the portolan charts might have simplified or distorted some features, that was never allowed to affect the overall geometric precision of the relative positions of the termini for pelagic voyages, since that underpinned the charts’ navigational function.
Roger and al-Idrīsī’s method of information-gathering, by interviewing multiple informants, would explain the unevenness in the quality of the map’s outlines. No amount of ‘improvement’ could have provided a single geodetic foundation comparable to the portolan charts’ self-correcting framework formed out of multiple pelagic courses.
There are a few similarities between the Charta and the Carte PisaneAccepted as the oldest surviving portolan chart, c.1270, its author and place of origin are unknown. It has been in the Bibliothèque nationale de France since 1839 (Cartes et Plans, B 1118) , for instance in the coasts around Tunis. 50 Nevertheless, it is difficult to see how al-Idrīsī’s own reported visits to the Maghrib could have had anything to do with those outlines. Moreover, the single most notable feature of the portolan charts – indeed their most distinctive coastal signature: the deep Gulf of Sirte – is only partially conveyed on the Charta where it is given a similar depth to that of two other, non-existent gulfs. Where the Charta is visibly more advanced than the Carte Pisane is in its portrayal of the Atlantic coasts, which lay outside the knowledge of that chart’s author.
A few instances of apparent agreement between the Charta and Carte Pisane might suggest borrowings from one or the other. But there are two separate arguments against that possibility: first, their respective purposes and, second, the Charta’s limited circulation.
A.3b.2. Different purposes of the Charta and the portolan charts
Both the Charta’s purpose and the way its information was gathered were fundamentally different to those of the portolan chart. Hierarchies of size and prominence had no place in the pelagically-fixed structure of the portolan chart, but al-Idrīsī was free to enlarge Sicily. The density of the inland detail confirms that al-Idrīsī and his patron were focused more on topography than hydrography, on geography rather than geodetic accuracy, and certainly not on the needs of pelagic sailors. In short, the Charta reflects primarily the outlook of a territorial ruler.
It is also instructive to compare the underlying cartographic structure of the Charta (with its apparent borrowings from Ptolemy) and the portolan chart. Each of the three was built up on a very different formal structure:
A.3b.3. Why the portolan charts were not used by al-Idrīsī
Roger II – or more realistically al-Idrīsī himself – spent fifteen years interviewing those who passed through the capital, Palermo, asking them about the geography of the world’s regions. A number of those informants must have been sailors. Had al-Idrīsī been shown a portolan chart, we can be confident that its user would have vouched for its accuracy and hence relevance for Roger’s project. Yet there are only fragmentary signs in the Charta of input from sailors and certainly no traces of the portolan charts’ many unique features.
It is always dangerous to argue from the absence of information but, in this case it seems justifiable because it is inconceivable that al-Idrīsī’s meticulous and well-documented, information-gathering exercise would not have revealed any nascent portolan chart that might then have existed. My failure to identify any traces of borrowings from a marine chart on the Charta, ties in with the majority opinion among researchers today. Tarek Kahlaoui, for example, concludes that "it is extremely difficult to argue for the Idrisian use of early portolan maps". 52
The significance of this cartographic silence – which has not apparently been noted previously – provides robust support for a portolan chart origin date of no earlier than 1154 (when al-Idrīsī began his final version) and around 1158 when he completed it). 53
A.3b.4. Why the portolan charts made no use of the Charta
The first and most obvious reason for this was the Charta’s inaccessibility. The 3.5-metre map was copied out in 70 sections, which were then distributed through an accompanying geographical text. The first time the full image is known to have been available was in a redrawing of 1928. Faced with the double impediments of a fragmented image and Arabic script, it is highly unlikely that anyone from outside the Islamic world would have seen the Charta or, if they had, would have been able to make sense of it – and certainly not at the time when the portolan chart was being developed. Hence, al-Idrīsī’s world map could not have served as any kind of inspiration for the portolan chart. 54
The second argument focuses on the lack of idrisian aspects in the portolan charts. For the Mediterranean and Black seas little could have been learned from the Charta by the creators of the charts. But the Carte Pisane’s author could have benefited from seeing the Charta’s Atlantic outlines. These include the Bay of Biscay, entirely absent from the Carte Pisane, as well as England (thus named), Ireland and, however roughly, some understanding of the North Sea coasts.
Hence the Charta cannot be considered relevant to the portolan-chart origins question: if it had preceded the portolan chart, it clearly did not inform that, and if, conversely, the Charta followed the portolan chart, al-Idrīsī was evidently unaware of it.
This, in a similarly oblique way, offers further evidence against any Arabic contribution in general to the origin of the portolan chart. Likewise, the Charta could have had no influence on the information set out in the LiberThe ’Liber de existencia riveriarum’, c.1210, written in Latin, is the oldest surviving guide to the Mediterranean, giving the distance and direction between places along the coast and across the open sea (Cotton MS Domitian A XIII, ff. 114r–129v) , the oldest surviving portolano (c.1210). 55
Having reviewed the possible cartographic antecedents to the portolan charts and found none that could have plausibly served as their inspiration, an alternative source for their geometric content needs to be identified. The solution proposed here is one that would have been invisible at the time and that will have left no trace: mental maps.
Unless some textual validation emerges it will not be possible to prove this mental-map thesis. But we can readily cite analogies with other unaided navigation techniques – both those recorded historically and some observed in recent times – which demonstrate far more impressive feats than those that will be attributed here to medieval sailors.
The reverse question might be even more relevant: how could those navigating the Mediterranean before the compass not have had their own mental maps? “There has probably always been a mapping impulse in human consciousness”, as J.B. Harley wrote on the first page of the first volume of The History of Cartography, “and the mapping experience – involving the cognitive mapping of space – undoubtedly existed long before the physical artifacts we now call maps”. 56
This investigation into the proposed mental-map source for the origin of the portolan charts considers a number of issues: human mental capacity (i.e., the brain functions relating to spatial memory), how mental maps work, and the use of mental maps for navigation (particularly by indigenous peoples). That will be followed by consideration of the skill-sets required when dealing with the specific circumstances found in the Mediterranean.
This section leans heavily on M.R. O’Connor’s, Wayfinding: the science and mystery of how humans navigate the world (2019) [Powerpoint, Slide 7]. 57 The author, an American journalist, ranges widely and deeply over the subject of human wayfinding. She shares her first-hand experiences in the company of Inuit hunters in the white landscape of the Canadian Arctic, Aborigines wayfinding in the Australian desert, and Oceanic mariners travelling vast distances guided only by the stars and waves. All of that is interwoven with a survey of the fast-moving developments in brain function research, focusing on the neurological basis of spatial orientation, and buttressed by interviews with the leading figures in the field. The science is not always easy but she takes us patiently through it. Though it is not directly concerned with Mediterranean navigation, this overview is a useful way into the theory and practice of human wayfinding.
Recent research into spatial orientation, as summarised by M.R. O’Connor, identifies two types:
The first is route knowledge, an ability to construct a sequence of points, landmarks, and perspectives that make up a path from one place to another. The traveller uses a string of memories of landmarks or viewpoints to recognize the correct sequence for getting from one place to another … The second strategy is called survey knowledge: the traveller organizes space into a stable, maplike framework, in which every point or landmark has a two-dimensional relationship to every other point ... Route knowledge relies on the traveler’s point of view and relationship to objects around them, what’s called egocentric perspective … Survey knowledge depends on what is called an allocentric perspective, a point of view that is objective, maplike … 58
Clearly, pre-chart Mediterranean navigation would have routinely involved a combination of the ‘route’ and ‘survey’ strategies. Following a remembered or prescribed course formed out of visible waymarks, on the one hand, and navigating ‘blind’ in the open sea aided only by a mental map of the inter-relationships of places and features aided by a mental wind compass, on the other.
As Anita Devineni points out, the spatial map identified in the hippocampus may serve “primarily to encode memories: events are always associated with a particular place, so linking the place to the event may be a handy way of ‘indexing’ your memories”. 59 Such an aptitude would have had great relevance for memorising a long sea voyage with its occasional sightings of land. 60
Could we be born with spatial memory recall? There are those who have suggested this might be the case. “While languages and navigational strategies may vary from one culture to another”, wrote John Edward Huth, “the wiring of the brain to create languages, mental maps, and other skills appears to be an intrinsic feature that we’re born with. Navigational skill depends on the interplay between memory, perceptions, and the mental map”. 61 David Lubinski thought that spatial ability “may be the largest unknown, untapped source of human potential”, while Alfred Ardila noted that “for thousands of years, human survival depended on the correct interpretation of spatial signals, memory of places, calculation of distances, and so forth, and the human brain must have become adapted precisely to handle this kind of spatial information”. 62
Given the origins of human evolution, it would be unwise to rule out the possibility that we have spatial navigation skills that have some equivalence to those being identified via tests on animals. Edward Tolman’s celebrated 1948 article, ‘Cognitive maps in rats and men’, 63 has been followed by other studies looking for parallels. Many animal abilities far exceed our own, whether in measuring time or maintaining direction over perhaps thousands of kilometers, but it is now thought likely that all species have some kind of a bio-compass that can respond to the earth’s geomagnetic field, even if, despite half a century looking for it, the evidence has not yet been found. 64 As the Inuit historian, Ken MacRury, explained about hunters in the Canadian Arctic: “They wouldn’t get lost. And the dogs never got lost, never. Fifteen or twenty years ago, the old Inuit couldn’t believe when people started getting lost. They couldn’t believe it was possible.” 65
The place in the brain where the mental map has to be looked for is the hippocampus.
The flurry of recent research into this area of the brain continues apace and doubtless in ten or twenty years’ time there will be far more certainty about the function of that and other areas associated with navigation and memory, for example the caudate nucleus. It is clear that the hippocampus is critical for both cognitive mapping and episodic memory. It can objectively represent the environment in three-dimensional space and allows spatial relationships to be inferred (e.g. by taking a short-cut).
The hippocampus is very malleable. It includes “head-direction cells, which discharge in relation to which way our head is pointed on the horizontal plane, and grid cells, which fire as we roam an environment and build a coordinate system for navigating”. 66 Essentially, the brain links its map of where things happened to memories of what happened. The key to the growth of its grey matter is experience, not time, and it responds particularly to complex environments. Growth can effectively start as early as six years old, and it can be observed to expand in response to formal memory exercises. The central relevance of the hippocampus to the conjectured mental map of the medieval mariner is obvious.
What is a ‘mental map’? The definition given in Wikipedia is as follows: “A cognitive map is a spatial representation of the outside world that is kept within the mind, until an actual manifestation (usually, a drawing) of this perceived knowledge is generated, a mental map. Cognitive mapping is the implicit, mental mapping the explicit part of the same process”. 67 Jeremy Black makes a similar distinction between ”'unmanifested mental maps' (those that exist only in the mind), 'manifested mental maps' (such as sand paintings and Australian aboriginals carvings), and printed maps". 68
On the other hand, in 1987 one meaning of ‘mental map or mental cartography’ had been defined in The History of Cartography, as “an image of the environment held in the mind to aid wayfinding or spatial orientation … [which] groups apparently carry in their heads as mnemonic devices”. 69 A possible current term might be ‘virtual map’ but, in the light of modern usage, that would be confusing and will be resisted here. Since this essay will discuss both the hypothetical content of sailors’ minds and its later manifestation in portolan charts, it would be unhelpfully pedantic to alternate Wikipedia’s distinction between ‘cognitive’ and ‘mental’ maps in those different contexts. ‘Mental map’ will therefore be used throughout.
Much could probably be learnt from the modern Vendée Globe, a single-handed, non-stop yacht race, in which participants sail around the world without the navigational aids taken for granted today. Earlier entrants were denied GPS and today they have to rely solely on sextants, paper maps and the stars; the magnetic compass is banned. A rather different example of traditional navigation is the story of the Hokule’a, a double-hulled Polynesian voyaging canoe, which covered nearly 50,000 nautical miles over a period of forty years, without the use of Western instruments, maps, or charts. 70
We no longer have access to medieval mariners but might it be possible to mount a research project that scanned the activity and physical development in the brains of these oceanic navigators undergoing the Vendée Globe challenge? [Although the all-important memories of past routes in the medieval instance would not apply there.] As a parallel exercise, the brains of the chart-less indigenous mariners of today (discussed below) could be studied, with non-sailing members of their respective communities acting as a control.
B.3b.1. London’s Black Cab drivers
The most obvious example of mental maps in action, albeit in an urban not marine context, is that of London’s Black Cab drivers. In what appears to those not involved to be an amazing feat, they create and then use a constantly updated, personalised mental map of 25,000 street names, 320 standard routes and 20,000 places of public interest, covering in all 20,000 miles [32,000 kilometres]. This process is aptly known as ‘The Knowledge’. Today’s drivers had learnt from an atlas, but they do not use GPS or carry paper maps. Their three- or four-year training is carried out when they are adults (usually supporting themselves with a job at the same time).
That needs to be contrasted with a medieval sailor’s focused experience, probably starting as a boy (when memories are more readily assimilated) and then spread out thereafter over perhaps half a century. Despite the fact that the majority of potential Black Cab drivers fail to complete the training, there are still 20,000 who have managed to pass and remain active today, keeping up with the steady stream of temporary or permanent changes in the London streetscape. In the light of that, it would be hard to contend that gaining a general (and in some parts detailed) mental picture of the Mediterranean would have been beyond the capability of a medieval navigator. 71
Initial research in 2000, and other studies since, have revealed that not only was the grey matter in the hippocampus of the cab drivers greater than that of London bus drivers (emphasising the importance of the cabbies’ decision-making) but that “the amount of time spent in the profession correlated with greater volume, proving the growth was accumulated”. This continued enlargement in brain function throughout the driver’s career reflects the fact that the stored information involved was both growing and changing. The memorisation process had involved transferring an existing street plan in its entirety into a mental construct. Conversely, the fact that people today increasingly rely on GPS to provide them with a precise location is apparently leading to a reduced volume in that same part of the brain. 72
For a comparison between the oral issues relating to the Black Cabs and the portolan charts, and specifically the need to keep their knowledge current, see L.2a. ‘Two modern usage comparisons: London’s Black Cab Drivers’.
The wayfinding skill and confidence of indigenous hunters who have adapted to their very different environments with varied navigation strategies, is at times extraordinary. Some of the Aboriginal ‘songlines’ – routes across the landscape linking features marking the tracks of the ‘creator-beings’ – are related to star positions. Where a Western astronomer might be able to name 100 stars, Aborigines, who had been steadily learning from childhood, can sometimes name thousands. When making long journeys across the Australian desert, the Aborigines were found to “possess some of the most precise orienting abilities known to man”. Their wayfinding skill involved “some kind of dynamic image or mental ‘map’, which was continually updated in terms of time, distance and bearing, and more radically realigned at each change of direction, so that the hunters remained at all times aware of the precise direction of their base and/objective” (reported by David Lewis). A person interviewed said he knew the directions “not by the sun but by the map inside my head”. One Aboriginal group in Queensland (and some other indigenous communities elsewhere in the world) do not have relative, subjective terms, such as left and right. Instead, they have sufficient confidence in their own spatial ability to use fixed, objective terms: North, East, etc. 73
In Oceania, the piloting techniques used by various island populations in the vast spaces of the Pacific Ocean, are ably covered by Ben Finney in The History of Cartography (Volume 2, Book Three). 74 In his introduction, on ‘Mental Cartography’, Finney summarises their attainments:
The navigational practices of Oceanians present somewhat of a puzzle to the student of the history of cartography. Here were superb navigators who sailed their canoes from island to island, spending days or sometimes many weeks out of sight of land, and who found their way without consulting any instruments or charts at sea. Instead, they carried in their head images of the spread of islands over the ocean and envisioned in the mind's eye the bearings from one to the other in terms of a conceptual compass whose points were typically delineated according to the rising and setting of key stars and constellations or the directions from which named winds blow. Within this mental framework of islands and bearings, to guide their canoes to destinations lying over the horizon these navigators applied vital information obtained by watching with the naked eye the stars, ocean swellsThe regular movement of rolling waves that do not break, steady winds, island-influenced cloud formations, land-nesting birds, fishing out at sea, and other cues provided by nature. 75
For the Caroline Islands, Finney quotes from Thomas Gladwin:
Everything that really matters in the whole process goes on in his head or through his senses. All he can actually see or feel is the travel of the canoe through the water, the direction of the wind, and the direction of the stars. Everything else depends upon a cognitive map, a map which is both literally geographical and also logical. 76
To Finney, the skills of the pioneering navigators, “must have included some competence in orienting and holding a course by reference to the stars, ocean swells, and winds, in dead reckoning, in sensing islands before they could be seen directly, and in incorporating newly found islands into some kind of cognitive chart”. 77 To test those methods, “since 1976 voyages over 2000 miles of open sea have been achieved”. 78
As another example, this time from the Canadian Arctic, Robert Rundstrom concluded that “the historical record and modern cartographic research both agree that most Inuit maps, extensively tested through a century of use by non-Inuit explorers and field scientists, were extraordinarily accurate renderings of the landscape as sensually perceived”. 79
We need to be careful about over-stressing possible direct parallels between the experience of Mediterranean sailors and indigenous mariners. For example, the Cook Islanders used a 32-point wind compass, as does the portolan chart, though those are presumably unconnected. 80 But neither should we deny the comparable demands made on all those who navigate over open seas seeking islands or distant shores. There must surely be some similarities in the solutions found and the mental capacity involved. There is no justification for assuming that the brains of indigenous navigators (whose skills have been observed up to recent times) worked in radically different ways to those of medieval Mediterranean sailors. It is always unwise to underestimate the ingenuity of those from a distant period, or a different culture, who either did not, or could not, leave a written record of their navigational practices.
One consideration that certainly links medieval navigation and indigenous wayfinding is that of necessity. In both instances, livelihood, safety, even life itself, depended on skill, memory, concentration, and careful observation when voyaging. In today’s world, “Navigation devices make vast reserves of distributed knowledge available to us in an instant. But, crucially, they never require us to possess information in our own memory in the way that successful navigators have been required to do till now”. 81
As one indigenous hunter put it: “Whereas most people like to go places, the Inuit people have to go places”. Another Inuit tracker, Taukie, gave an insight into the paired skills of memorisation and recall: “When we’re taking in details in our head, we try to look at the little stuff. When we travel past something we look behind us because it looks different from that angle. Every detail we are trying to put into our heads.” 82
Not all memorisation is intentional. In the Wikipedia entry for ‘Memory’ (seen 7 March 2020) there is the following statement about “the unconscious learning or retrieval of information by way of procedural memory, or a priming phenomenon”. Priming is explained as “the process of subliminally arousing specific responses from memory and shows that not all memory is consciously activated, whereas procedural memory is the slow and gradual learning of skills that often occurs without conscious attention to learning”. The Inuit tracker and medieval pilot alike would no doubt have committed material to memory both consciously and, at other times, without being aware of it.
As Barry Cunliffe pointed out, “It was 9000–5000 BC that saw the beginning of seafaring in Europe … The Phoenicians were the first of the Mediterranean States to enter the Atlantic in the 10th century BC and their main home port was Gadir on the Atlantic”. 83 Another source locates the appearance of professional mariners and established routes in the Bronze Age,
the time where both archaeological records and texts confirm the beginning of the maritime specialization, that is, the appearance of sailors as distinctive professionals ... We can ascertain the existence at the IIIrd mill. BC, and especially for the IInd mill. BC, of established commercial waterways as it’s evidenced through the Ulu Burun and Cape Gelidonya wrecks. 84
Thus, for centuries, indeed millennia, besides proceeding along a coastline (cabotage), ships had set sail across the Mediterranean (pelagic voyages), often out of sight of land, without the aid of navigational instruments, except perhaps a log line. 85
Empires inexorably rise and fall, and maritime trade can be disrupted. But that was too vital for the parties concerned for it not to be continued, even if by indirect means. Hence there is no reason to suppose that seafaring practices – say those found effective by Roman pilots – would not have continued, possibly with improvement, up to the Middle Ages. Hence it is relevant to take note of what is known or conjectured about navigation in the ancient world.
We are fortunate that, with the highly literate classical world of Greece and Rome, we start to encounter written accounts, which are disappointingly missing for the medieval period. In his doctoral dissertation Danny Lee Davis made a thorough study of textual sources from the classical period. “In ancient literature”, as he explains in that major revisionist thesis:
“the oft-repeated themes of storm, shipwreck and death at sea led to the popular assumption among scholars that seafarers developed habits to minimize their exposure to this hostile element—hugging the shore to avoid the open sea, putting in at night, sailing only in summer, and using ‘seafaring manuals’ to help guide their way. While several recent studies have made some strides in overturning this overly simplistic view by highlighting aspects of navigation in certain areas and in certain periods, the ‘standard model’ lingers in both scholarly and popular imagination … My research concludes that both coastal and open-sea sailing were matters of routine in the commercial sector, that commercial seafarers did indeed sail at night and employ the stars to deduce navigational information, that winter sailing was a widespread practice, and that crews employed navigational strategies to weather storms, usually successfully.” 86
When writing about navigation in the later Middle Ages, Renard Gluzman confirmed Davis’s account, noting that “crossing open water was an integral part of any long-distance voyage … Venetian vessels sailed greater distances and much farther from the coast than had previously been thought”. 87
Among Davis’s many interesting conclusions is the following. “It is highly unlikely that any Greek or Roman seafarer used one of these works [periploi, the forerunners of the portolani (Singular ‘portolano’ and more usually called ‘portolans’ – which can be confused with the charts) these were medieval guides to the coastal places around the Mediterranean, listing the distances between them. They also include open-sea (pelagic) routes] … for the purposes of navigating from place to place”. 88 Davis’s views were supported by Carmen Obied in her 2016 doctoral thesis: “Regarding ancient knowledge of navigation, extant evidence points towards a practical knowledge of seaborne travel and orientation which developed through ‘mental-maps’ based on experience and practice, and was likely predominantly transmitted orally”. 89 Much of the above is corroborated by Pascal Arnaud whose point of departure was “the assumption that implicit or tacit knowledge structures have been used in ancient times to form cognitive maps for orientation”. He elaborated that, commenting that Classical Greek geography “was based upon durations rather than distances, and upon an original perception of orientations and directions. Thanks to that knowledge, based upon the repetition of experience through generations and apprenticeship, they were able to sail the blue sea without maps or instruments”. 89a
Instead of enquiring whether the Greeks and Romans had marine charts, we should rather ask, did they produce graphic versions of the charts they apparently held in their heads, to which the answer is that there is no evidence of that.
If landmarks were not going to be available as a guide, in the period before the portolan chart, pilots had to know beforehand, fairly precisely, in which direction(s) to head and roughly how long it would take to reach their destination. Another obvious point, which might be overlooked, is that for land to be recognised it had to have been anticipated. When planning a voyage, the pilot would need to take account of intervening islands, note where the voyage might be broken, or water and supplies shipped, and in particular, anticipate the dangers that were likely to be encountered en route. Any lesser assumption is surely untenable. Unless they had followed memorised courses, no routine trading, pilgrimage or military voyages could have taken place. 90 Indeed, these ‘sea roads’ are well documented from surviving texts and wrecks (which were more likely to have been caused by weather conditions than poor seamanship). The following pair of assertions that underpins this essay is therefore proposed:
Nobody would have routinely left port without knowing the direction to take, any islands or dangers likely to be met with on the way, and the approximate distance and time involved to reach the planned destination
Nor, in the period before the portolan chart and the magnetic compass, would they have done so unless they were confident of being able to determine at least one direction when in the open sea
So, lacking the information a chart could have provided, the medieval sailor had to depend on his own experience or on the instructions he could obtain orally from others. This might have been his shipmates or those he met in port. By definition, no-one travelled more widely in the Mediterranean than its sailors. And nowhere was there more international mingling than in its ports, for instance those on Italy's west coast, by common consent the birthplace of the portolan chart.
The mental abilities required for medieval navigation would fall into those two types described earlier in the discussion on mental maps: respectively, route knowledge and landmark orientation. 90a Because of the risks involved in open-sea journeys, navigators needed to acquire a packed memory of courses run and dangers avoided, backed up by the visual appearance of the numerous headlands, bays, river estuaries, coastal and island outlines, etc., they had seen. William Bourne, in his Regiment of the Sea (1574), noted that a shipmaster should “be a good coaster, that is to say … knowe every place by the sight thereof”. 91
Cunliffe wrote that:
For any sea or stretch of coast, the accumulated sea lore would have been vast. It was essential to the well-being of maritime communities that it was kept up to date and passed on from one generation to the next. In preliterate times this would have been done by word of mouth, possibly in the form of chants or songs, or at least in rhythms that allowed the instructing to be committed to memory. 92
The record of each newly completed voyage would need to be memorised, to join those from previous courses run, since remembering those details would be crucial when any came to be repeated.
Danny Lee Davis makes a number of interesting observations on routes actually taken as compared to those theoretically described, a distinction not generally recognised by historians:
Sailing vessels rarely traveled in straight lines. Instead of fixed routes sailing masters chose to sail within seasonal corridors of movement in which conditions were most favorable for efficient forward movement. 93
He also pointed out that “No route, no matter how short or how often made, was ever repeated precisely. At odds with this notion, however, are the ubiquitous maps of finely delineated sea routes we find in studies of ancient seafaring, trade and economics”. 94 In other words, the focus on simplistic, generalised descriptions of pelagic routes may be misleading. Though his remarks derive from a detailed examination of Classical navigation (well supplied with textual sources), his elaboration of the argument is worth repeating for its likely application to the largely undescribed medieval context.
Based on our source material, and taking into account the multitude of variables involved in each voyage even in optimal conditions, we should instead envision ancient sea ‘routes,’ whether short- or long-haul, as wide maritime corridors of general movement between one place and another. These corridors were defined by environment and meteorological factors, by technological responses to the demands of sea travel and by the ever-shifting realignments of trade trajectories throughout the seasons, years and centuries. The aggregate effect was of loose bundles of overlapping lines connecting coastal and island nodes, and not of straight, single paths overlaced multiple times. 95
We cannot hope to understand how medieval sailors navigated with a chart without knowing how they had managed without one. In other words, what did portolan charts offer pilots that they didn’t already have?
Prior to the chart and the magnetic compass, medieval pilots would have needed to interpret the sensory information they were receiving so as to answer three basic questions: where are we, where do we want to go, and how will we best get there? Navigating with a wind compass 96 might have been equivalent to a blind commuter today finding their way to work by means of remembered features and sensual clues, not available to their sighted colleagues. The focus needs to be more on those aspects, undescribed and almost entirely lost, rather than the well-documented, tangible mechanical aids.
Davis offers a relevant parallel from the Classical world:
Historical sources reveal an occupation of low social status that nonetheless required a prodigious set of complex skills and a practical knowledge earned from numerous hard years spent at sea—seamanship, crew leadership, maritime geography, winds, currents, weather prognostication and nautical astronomy, among others. Together these skills and knowledge constituted the “steersman’s art,” ta kybernetika, or the ars gubernatoris. 97
When establishing the approximate position at sea, the 12th-century mariner would have used ‘dead reckoning’: the ability by long experience to estimate the direction and distance covered, by relating the ship’s apparent speed through the water to the elapsed time, with the use of astronomical and other indications. He would have had no instruments, apart from a log line. It seems likely that the magnetic compass was developed after the time of the first portolan charts 97a and the hourglass or sand clock somewhat later still. 97b To determine the ship’s position, the calculations of distance and direction (using such things as the angle of the swellThe regular movement of rolling waves that do not break) were augmented by astronomical aids, and particularly the known bearing of the expected wind (which had provided sailors with a theoretical compass for centuries before they first saw a magnetic needle).
When estimating the ship’s speed, allowance would be made for a following or adverse wind, the swell, any current there might be, and the effect of tacking. As far as direction was concerned the mariner had to select the desired heading, maintain it, and, if forced off course, regain it. For this, the toleta de marteloio, ‘a trigonometric reduction table to aid navigation by dead reckoning’, 98 would have been relevant but it is not clear how widely it was used to calculate the actual course sailed when tacking into the wind. The oldest known textual reference to it is from 1295, though that does not mean it could not have been in existence earlier. 99
When cloudy conditions obscured the sun or the stars, navigators would have had to rely on their own senses. Even if, when calculating distance and determining direction, they may not have had the equivalent of perfect pitch in music, it must surely have been the case that those senses would have been heightened first in training and then through constant use. Medieval pilots would have been attuned to their surroundings far more acutely than those of us in the developed world today, even experienced mariners. The sophisticated layers of personal and very detailed information, which must often have been retained in visual form, would also have included a wide variety of sea sign. The following would be a probable, if incomplete, list of those:
Approaching land: signs such as orographic clouds (created by the topography of an island that might still be out of vision); sightings of birds, fish or aquatic mammals; 100 driftwood, seaweed or floating vegetation.
Coastal profiles: fixing location in relation to the appearance of a coastline would have depended on reference to what must have been a large part of a navigator’s visual memory
Currents: the portolan charts could have introduced a symbol for areas with strong, regular currents, for example between some islands and the mainland, but they did not. So there is no warning on the charts, for example, about the strong tidal currents in the Strait of Messina dividing Italy from Sicily with its Charybdis whirlpool, nor the Gibraltar and Dardanelles straits. The implications of those would have to be learned but, once experienced, would surely not have been forgotten
Depths: checked by soundings with a lead line, perhaps revealing the bottom deposit which might help to identify the area; measured soundings were only introduced to charts in later centuries, but the charts’ hazard symbols served a related purpose by highlighting dangerous shallows
Prominent natural features: when “viewed against the sky would have been fixed on the mental map carried by all successful mariners” 101
‘Set and drift’: a combination of wind and current that could be pushing the ship off its course
Speed: perhaps estimated by leaning over the side and watching the bow wake, or by using a log line
Swell: wind-generated waves which can continue to reflect a wind even when it has not blown for days 102
Water: colour, appearance, even smell 103
Weather: knowing what weather to expect and being able to anticipate dangerous conditions
Winds: which winds (both seasonal and diurnal) to expect; the trim of the sails from which the direction of a constant wind could be read
Wind compass: the mental wind compass is described in great detail in a separate essay – The mental wind compass of the medieval Mediterranean: the rediscovery of its structure and interpretations of its use – and summarised earlier in this one. 103a Prior to the introduction of the magnetic compass, the ability to ascertain directions at sea, by relating observed astronomical and other phenomena to a memorised compass, was a pre-condition for navigating in the open sea
Even with a compass and other instruments, those senses and perceptions would still have been essential for safe and effective navigation right up to the time that radar, echo sounding and satellite navigation introduced the first fundamental changes into navigation. 104
Assertion: Details of pelagic courses in the Mediterranean must have been held in sailors’ memories for millennia, hence a 12th-century sailor would have been using some kind of mental map, in the absence of any textual or graphical guide
Compared to other indigenous navigation – in the Pacific, Arctic, Australian interior, North Atlantic, etc. 105 – the Mediterranean has a number of advantages. In the first place, its encircling coastlines provides a spatial framework, as Danny Lee Davis pointed out in the Classical context:
The intricate coastal rim served as the focus of navigation conceptualizations from an early date, functioning as the primary frame of reference in the ancient geographical tradition and reaching its most pragmatic expression as early as the sixth century BC. in the subliterary genre known as the periplus, or coasting voyage. 106
The Mediterranean provides numerous islands to serve as waymarks or break longer journeys, and a shoreline of some sort would nearly always appear after a few days sailing. 107
In some areas, coasts would have been constantly visible. Examples are the northern part of the Sea of Sardinia (taking in the Franco-Italian coastline); the western half of North Africa; Sicily and southern Italy; the Adriatic; Greece, Crete and the Aegean; Cyprus and the southern coast of Asia Minor and the Levant. However, “for over perhaps one third of the Mediterranean Sea there is no sight of land even in optimal meteorological conditions”. 108 That would also apply to most navigation across the Black Sea.
However, in other very different marine environments, such as Oceania, and particularly the Marshall Islands, navigators had to rely on the distinctive pattern of the waves (‘wave piloting’) to deduce where the islands are. Might areas of the Mediterranean have had their own navigational ‘signatures’ to aid in locating the ship’s position?
The Mediterranean mariner’s mental map coupled with memorised pelagic experience should have enabled any land-sighting to be recognised and identified, and what might lie over the horizon to be anticipated. To achieve that, he would probably have needed to memorise only a proportion of the 2,000 place-names found on a typical portolan chart. More important would have been the storing in memory of a number of long courses, as well as many other shorter ones within sight of land: for instance, sections of coastline or links involving islands. It is highly unlikely that medieval pilots had an encyclopaedic knowledge or had sailed all over the Mediterranean, although much of their understanding would doubtless have been acquired orally rather than through direct experience. As Grazioso Benincasa An ex-ship captain, he left us a range of clearly-drawn charts and atlases (1461-82) and a written portolano (1435-45) states in the introduction to his portolano (Plural portolani and more usually called ‘portolans’ – which can be confused with the charts) these were medieval guides to the coastal places around the Mediterranean, listing the distances between them. They also include open-sea (pelagic) routes of the Adriatic, Aegean and Black Sea (1435–45): “I will make mention of ports and places … according to my memory … These ports and the appearance of land features are not drawn from a chart but have been found out and viewed with my own eyes”. 109 The mental map thesis takes those individual limitations into account, positing an origin formed out of shared, rectified knowledge.
To put in context the mental effort required to learn and retain the details of each course, it may be relevant to mention comparable feats of memory. The Quran has 77,000 words (which are memorised by millions of Muslims, thus allowing them to use the title Hafiz, for as long as they continue to remember it). The Bible has around 750,000 words (though that seems to be beyond all except autistic savants). As mentioned earlier, the London Black Cab drivers have to memorise 25,000 streets, and much more besides. 110 Some examples from indigenous communities that continue to hold to their old ways, have already been described. 111 Had the mental load for medieval mariners been equivalent to that of London’s Black Cab drivers, devout Muslims or indigenous navigators, which is unlikely, then we could expect their hippocampus to have expanded in a similar way.
A medieval sailor may also have had one unnoticed advantage. It is justifiable to consider if a lack of literacy might have freed up mental capacity for memorised experience in place of book learning, or, perhaps more plausibly, the corollary of that which sees developing literacy as demanding its own part of a finite space. It is possible that what is known as the ‘Homer Simpson Effect’, where new information pushes out old, may have relevance, not only for neuroscience but also the mental map posited in these pages. 112
In 2009, the French cognitive neuroscientist, Stanislas Dehaene, advanced what he admitted was a speculative argument:
Reading invades the neuronal circuits destined for another use and probably brings about the loss of some of the cognitive abilities that were handed down to us by evolution... Thus, reading acquisition possibly reduces the cortical space available for our other mental activities. The neuronal recycling hypothesis makes us wonder if our illiterate ancestors had visual skills that we have now lost.
He also noted how traditional hunter-gatherers ‘read’ the natural world, in ways where we today are illiterate. “It is possible that reading animal tracks is the cortical precursor for reading.” 113
Subsequent research by a team led by Maria Wimber reinforced the Homer Simpson effect, finding that “remembering induces forgetting by actively suppressing the brain activity encoding similar, interfering memories. They believe this is an adaptive mechanism that increases the likelihood that we will successfully encode and remember only the most relevant information”. In other words, to be fully effective the mental storehouse of medieval pilots would need to have been both carefully edited and refreshed. 114
On their own, a sequence of coastal observations would never have produced a coherent chart of the Mediterranean, since there would have been no way to relate opposite coastlines to one another. Only voyages – across both the narrower seas and the longer stretches out of sight of land, and with carefully recorded direction and duration – could have bound the extremities together and linked them, both to one another and to the intervening islands. That process would have created a nexus of nodal points (usually headlands) to bind the trigonometry into a plausible whole. In commenting on orally-transmitted pelagic descriptions, Cunliffe explained that this was the “way networks of knowledge were constructed”. 115 Numerous adjustments, when for example landfall was not where it was expected, and the infilling of the intervening detail via coastal observation, must also have played their part. But the notion that anybody sailed their way around the Mediterranean in an attempt to create a general chart, or indeed that they might have even thought of doing so, must surely be excluded as a wholly anachronistic concept.
Most historians of the Classical world take for granted that sailors used mental maps, backed up with oral transmission. As Cunliffe observed, a sailor “had to carry in his mind a cognitive map in which to position himself at all times”. 116 There is no reason to suppose that those traditions would not have continued, uninterrupted, into the Middle Ages. On the contrary, what could have caused a total break in the orally transmitted component of navigation lore, given that the trade in which most seamen were involved would have continued without extended interruption? In what significant ways would sailors’ needs or abilities, and the physical environment itself, have changed over a thousand years? It is being argued here, based on the premise of mental maps, that, in one very real sense, the portolan charts’ gestation period should be measured not in centuries or decades but in millennia, in other words from the time that ships started to follow repeated open-sea routes for trading purposes, and the records of those pelagic voyages began to be memorised.
Underlying this essay are two assertions: first that whenever information has been vital, there would have been a strong incentive to commit it to memory, and, as a result, that an experienced medieval mariner would have had a workable mental map of the Mediterranean. And second, as an extension to that, whoever first imagined the idea of a portolan chart, and anyone using the prototypes, would have already been skilled in navigating without one.
It is inconvenient for historians but, by its nature, a mental map leaves no physical trace. Nevertheless, previous commentators have already given serious consideration to the part that mental maps might have played in the origin of the portolan chart, even if only partially and certainly not as the sole source. For instance, Roel Nicolai suggested that “It is not improbable that Lo compasso de Navegare ’Lo compasso de navegare’, c.1260-96, written in Italian and apparently designed for sailors, is much more detailed than the earlier ’Liber’ (Staatsbibliothek, Berlin, MS Hamilton 396) also contains some distances that were estimated from experience, notably Peleio [pelagic courses]”. 117 Ramon Pujades also considered the possibility of a mental map, although he does include caveats:
Nonetheless, in order to produce a reliable chart using no data other than those of distance and directions and the visual memory of experienced seamen, first it would have been necessary to compile the information culled from a substantial number of crossings, because perfection in terms of representation could increase only as the number of points grew that could be located in respect to each other with relative precision, which in turn was directly related both to precise calculation of distance and finely-tuned determination of direction. 118
As a general comment, Joaquim Alves Gaspar and Henrique Leitão observe that pre-Mercator nautical charts:
carry inside their internal geometry the imprint of the activities of pilots on board, that is, a ‘signature’ of their artisanal origin and of the techniques used to navigate ... nautical charts were deeply influenced by the practices of the artisans who used them, but, simultaneously, such influence was almost invisible to contemporary scholars and present-day historians. 119
To counter the argument that the precision of the sailors’ knowledge of pelagic courses would have been insufficient for effective navigation, recent research offers a contrasting view. In his study of the pelagic courses described in the early 13th-century LiberThe ’Liber de existencia riveriarum’, c.1210, written in Latin, is the oldest surviving guide to the Mediterranean, giving the distance and direction between places along the coast and across the open sea (Cotton MS Domitian A XIII, ff. 114r–129v), Gaspar notes that “13 out of 18 directions are exact when expressed in terms of a wind rose of sixteen points … Furthermore, the 13 null-error directions include most of the tracks of 200 miles or more, as well as the two longest routes of all, those from Alexandria to Patera (650 miles) and from portus Bocchi to Bugea (700 miles)”. 120
The only plausible sources of that pelagic knowledge would have been the following:
From which it surely follows that:
It was the stars and the sun that provided sailors with more precise and reliable confirmation of the direction they were sailing – as long as the skies were clear, and, as far as the sun was concerned, at the important times of the day. Not that extracting the required information was straightforward. At sunrise and sunset, for example, the sun only identifies east and west precisely twice a year, at the equinoxes. At other times, increasing with both latitude and the passing months, the rising and setting of the sun will indicate noticeably different directions. As a result, the sun in the northern hemisphere will rise and set further towards the north-east and north-west as it heads to the June and December solstices. A further consideration is that the sun’s meridian passage occurs up to 15 minutes before or after noon, but that refinement would probably not have been noticed by a medieval mariner.
Once a single direction had been determined, all the others could be interpolated by reference to the sailor’s mental compass (see the following section). Time could also have played a part in the direction-finding by determining when the mid-points were reached between dawn and midday, and between midday and sunset.
The disadvantages in measuring direction at those four times of the day, or by the North Star at night, when on a boat that was perhaps rolling or tilting, should not be minimised. Taking into account also the likely imprecision of the solar sightings, and the brief period those remained relevant, it seems likely that observing the direction of the swellThe regular movement of rolling waves that do not break, which might remain constant for long periods, along with other sea signs, 121a might have sometimes proved more effective direction-finding aids.
At night, the main guide was the North Star (also known as Polaris or stella maris), found in the asterism of the Big Dipper (or Plough) within the constellation of Ursa Major. All mariners would have known how to extend an imaginary line upwards through the asterism’s front two stars, continuing that line for five times the distance between those in order to find the bright Polaris star. Even though it provided a bearing for approximately half the time only, unlike the compass it had the great advantage that it did not vary with position nor change noticeably over time. For those reasons, it must have remained the ‘gold standard’ for some years after the magnetic compass was introduced.
Leaving aside such astronomical assistance, there is plenty of evidence that medieval mariners were skilled at dead reckoningEstimating the direction and distance travelled by relating the ship’s apparent speed through the water to the elapsed time, so as to find the position at sea, with an ability to hold a constant mental course on the open sea. 122
When discussing the origin of the portolan chart, the mental wind compass is inseparable from the mental map that is being proposed as the chart’s ultimate source. As Ramon Pujades pointed out: “The question of the wind network thus becomes a fundamental aspect as regards the issue of the origins of nautical charts”. 123 It has already been asserted that mariners would never have set out on pelagic voyages without knowing what lay beyond the horizon, but neither would they have done that unless they were confident that they could recognise at least one direction once they lost sight of land. Put simply, without a mental compass there could have been no pelagic sailing. From time immemorial, open-sea pilots would have found ways of dividing and subdividing the horizon into equal-sized arcs, whose width would have matched the precision of their direction-finding abilities.
Determining direction is arguably the most important single aspect of open-sea navigation. Distance and time can be important, and forewarning of offshore dangers could never be ignored. But knowing where you are and where you need to go are crucial. If you are, unknowingly, heading in the wrong direction, other considerations have little relevance.
Since the Classical period, there had been alternative systems made up of eight or twelve winds. By around 1200, or probably earlier, a schema had been developed with eight named winds at its core. Unfortunately, the sparse evidence available about that wind compass is both conflicting and incomplete, and past attempts to interpret it unconvincing. It seems that the workings of the system were never written down; at least no relevant text has been found [Powerpoint, Slides 8 & 15].
Some months spent analysing the 1,287 directional statements found in the mid-13th century Lo compasso de navegare’Lo compasso de navegare’, c.1260-96, written in Italian and apparently designed for sailors, is much more detailed than the earlier ’Liber’ (Staatsbibliothek, Berlin, MS Hamilton 396), in partnership with Roel Nicolai, produced a report, which has been published separately online. 124 Roel’s analysis of the terms used in Lo compasso provided, for the first time, the full complement of directional instructions. This revealed that there must have been 128 directions (some as precise as 2.8 degrees). The rigid uniformity in those statements demonstrates a sophisticated, well-established mental compass. This could only have been derived, orally, from mariners. However elaborate that system appears to us, it is difficult to dispute that it must have been used (to varying levels of precision) by pelagic sailors. Why, otherwise, would it have been devised?
What has not been found, though, is the certain sequence of those subdivisions, and Roel and I had to settle, amicably, on different interpretations. Nevertheless, we were able to conclude that in the medieval Mediterranean there was a level of direction-finding ability sufficient to make pelagic voyaging acceptably safe. Furthermore, such proficiency must have been widely spread among pilots, and not the preserve of a select few.
Historians have long been divided over the question of whether the magnetic compass was involved in developing the portolan chart – possibly even being a precondition for that – or if, alternatively, it played little or no part in that process at all. In the light of recent research, it makes more sense to review the evidence rather than spend time exhuming old arguments. 125
The status of the LiberThe ’Liber de existencia riveriarum’, c.1210, written in Latin, is the oldest surviving guide to the Mediterranean, giving the distance and direction between places along the coast and across the open sea (Cotton MS Domitian A XIII, ff. 114r–129v) in the discussion about the introduction of the compass is far from straightforward. The discovery by Joaquim Alves Gaspar that the pelagic statements in that work appear to comprise both those that had been determined astronomically and those deriving from a magnetic reading is of considerable significance for the charts' origin. In his estimate, the majority of the 159 pelagic tracks in the Liber’s summary reflect traditional astronomical methods, whereas deviations in other bearing statements betray a bias (unrecognised of course at the time) that resulted from the use of a magnetic needle. 126
This glimpse into the crucial transition in navigation represented by the introduction of magnetic readings alongside those obtained by traditional methods carries with it further implications. Gaspar has also confirmed that the distances (which form one half of those pelagic statements) could only have been derived from a cartographic document because they are no more than straight-line measurements that do not reflect how those courses might have been sailed in practice. 127
If the Liber's text and the hypothetical graphic predecessor of the portolan chart appeared at approximately the same time, there would then have been a gap of perhaps seven decades before the appearance of the Carte PisaneAccepted as the oldest surviving portolan chart, c.1270, its author and place of origin are unknown. It has been in the Bibliothèque nationale de France since 1839 (Cartes et Plans, B 1118) around 1270. Analysis has shown that by that time all the directions had been determined magnetically.
The earliest known reference to the use of a magnetised needle in the Mediterranean was made by Alexander Neckam in his De utensilibus and De naturis rerum, both supposedly written about 1190 (though possibly somewhat later), perhaps close to the moment of the portolan charts’ inception. From its original form, as a magnetised needle floating in a bowl, this would develop into a dry-pivot compass pointer, which would have moved freely over a circular diagram, probably calibrated by means of abbreviations for the wind names. The added convenience of this more reliable compass, fixed on the fore-and-aft line of the ship close to the helmsman, seems to have been signalled by Petrus Peregrinus in 1269. 128 However, there are differing accounts of the sequence and dating of the respective developments.
In Julian Smith’s view, “No twelfth- or thirteenth-century author considers the magnetic compass a novelty. Most refer to its use on board ships in a matter-of-fact way, leading historians to suggest that the instrument was already commonplace in Europe by the mid-twelfth century.” 129 This observation on the magnetic compass implies that the transition from astronomical to magnetic navigation was widespread, speedy and straightforward. But was that definitely the case? There is a need to differentiate between the first appearance of the magnetic needle and the general adoption of that device, while at the same time distinguishing the separate introductions of the needle and, later, the compass card that was required for its effective use (on which see later in this section).
Other estimates of the compass’s introduction were more cautious, such as Roel Nicolai’s conclusion “that the mariner’s compass only came into widespread use in the course of the fourteenth century”. 130 That was supported by Ramon Pujades, who found no mention of the compass as a unit in notarial documents involving mariners before 1349, although that first instance could well refer to an instrument that had been in the possession of the sailor concerned for some time. 131
Separate from, and for the present purpose, of greater relevance, is the issue of the way in which the compass needle was used. Neckam had written about sailors touching the lodestone with a needle, adding significantly, “when in cloudy weather … [or] in darkness”. 132 He had learnt about the magnetised needle in Paris and seems to have had no direct experience of its use. However, the much travelled Guyot de Provins – who visited Constantinople and Jerusalem, and may have been on one or more crusades – included a number of passages describing its use in similar terms, when he wrote for example, around 1204:
When gloomy darkness hides the sea
And one no star and moon can see
They turn on the needle the light,
Then from the straying they have no fright
For the needle points to the star. 133
From those references it might be inferred that, in that initial period, the magnetic needle was used only when there was no alternative. However, in 1219 Jacques de Vitry, who had arrived in Acre as its bishop three years earlier, included in his ‘History of Jerusalem’ a description of the iron needle (acus ferrea) as being “very necessary for those that sail on the sea”. 134 That seems to be the first instance in which there is no stated qualification about the occasions on which it was used.
If in 1190 and 1204 the magnetised needle was regarded as a fall-back option, but by 1219 it was being referred to as an essential navigation aid, that suggests – albeit on that very limited evidence – that there was a step-change in the early 13th century in the way that the device was viewed and used. This is of considerable relevance for the origin debate, since that is also close to the period in which both the portolan chart’s progenitor and the LiberThe ’Liber de existencia riveriarum’, c.1210, written in Latin, is the oldest surviving guide to the Mediterranean, giving the distance and direction between places along the coast and across the open sea (Cotton MS Domitian A XIII, ff. 114r–129v) , which evidently took its directions from a marine chart, are thought to have appeared.
It is natural to assume that the magnetic needle must have given more confidence to the process of direction-finding. Once someone had sailed with a compass, perhaps on an overcast day or at night, it might be wondered how readily they would have reverted to what could have seemed the cumbersome assessment of natural phenomena. But the early compass did have considerable drawbacks. In the first place there was more involved than just reading off the divisions on a circle (assuming it had one). During the first years, before the dry-pivot form was developed, the needle would have had to be retrieved from where it was stored, placed on a straw or sliver of wood, and floated on a bowl of water. Only then could the direction be read off.
That was just an inconvenience but there were larger difficulties. The astronomical markers sailors used are, broadly, unchanging. The North Magnetic Pole, on the other hand, will deviate in various ways from true north (the Geographic North Pole), depending on location (declination) and the passing of the years (variation).
It is therefore likely, in the early period, that the compass needle was a supplementary aid, rather than an entire replacement for the astronomical observations used for direction-fixing. This meant that mariners could, unknowingly, have been using two separate ‘norths’. The difference between those might often have been minimal but around the year 1200 the magnetic declination in the central Mediterranean was as much as 10 degrees east, with lower figures to either side of that: six for Portugal and four for the Levant 135 For generations, navigators had managed with the sun and stars, but now they were asked to transfer their trust to a device whose incomprehensible working must have seemed quasi-magical. 136 Unless it is contended that a discrepancy of up to 10 degrees would not have been noticeable within the limited accuracy some might assume could have been achieved at the time, 137 it needs to be accepted that medieval mariners would have been at least partially aware of the differing results from the alternative direction-finding methods, even if the reasons for those would not become clear until long afterwards.
It also has to be remembered that the addition of a circular card to provide visual recognition for some of the major directions seems to have been a significantly later invention. There are conflicting accounts of when the compass card first appeared, but the earliest mention seems to be the attribution of the invention to Flavio Gioja around 1300. Another reference is found in Francesco da Barberino’s, Documenti d’amore (1306–13), in which he described the lodestone and needle as indispensable, without specifically referring to the compass card. 138
By contrast, Wallis and Robinson concluded that the first reliable reference was “by Francesco de Buti in 1380, and the first illustration in Gregorio Dati’s manuscript ‘La Sfera,’ c.1422”. 139 Even then the card is unlikely to have included much detail, perhaps no more than the quarter winds, as in a version of a 32-point system with no lettering in the c.1475 version of Dati’s ‘La sfera’ in the Library of Congress. It would be centuries before the compass card provided more than just a framework, to which the further subdivisions of a mental wind compass would need to have been mentally added.
For the compass proper to have gained a degree of trust equivalent to that of the earlier tried and tested mental methods, users would have needed first to recognise those discrepancies and then to compensate for them. It seems that that is indeed what they did, even if only selectively.
Discussion about the introduction of the compass has tacitly assumed that that development was not only a major benefit for navigators but a turning-point for the history of navigation, perhaps making the creation of the portolan chart possible in the first place. For navigation, it clearly had obvious advantages, for example in maintaining a constant direction (providing allowance was made for wind and current) or to confirm a bearing when it was possible to look back at a receding coastline. But the advantages should not be overstated. The compass could confirm the relative positions of features, provided they were intervisible. However, it alone would not have told the helmsman where he was when in the open sea, since that relied just as much on estimates of the distance travelled and the bearing previously followed, or the position of what was known to lie ahead over the horizon.
Nor should we necessarily start with the assumption that the infallible accuracy of the magnetic compass – putting to one side its initially unrecognised variation – would have swiftly replaced the direction-finding abilities of even the most experienced mariner. Unless the theoretical 2.8° precision seemingly revealed by Lo compasso’s’Lo compasso de navegare’, c.1260-96, written in Italian and apparently designed for sailors, is much more detailed than the earlier ’Liber’ (Staatsbibliothek, Berlin, MS Hamilton 396) pelagic descriptions is interpreted differently 140 surely the pendulum has swung, at least partly, in the other direction, as an endorsement of the wind compass, and the relevance of the refined navigational skills required for its use. Set against the pole star (whose progression is sufficiently slow as to be undetectable during a sailor’s lifetime) and the predictable movements of the sun and other stars, combined with what the smallest of the wind direction divisions seem to tell us about the precision achievable by at least some of the pilots of the time, it can reasonably be asked: why would they have wanted to throw away that hard-gained mental and sensorial knowledge?
Thus, instead of altering the directions tied to the venerable mental wind compass, it seems that at some point in the 13th century a once-only decision was taken to swing the cartographic image 9 degrees clockwise, thereby re-aligning the entire chart in a single move. That is why an east-west line on the Carte PisaneAccepted as the oldest surviving portolan chart, c.1270, its author and place of origin are unknown. It has been in the Bibliothèque nationale de France since 1839 (Cartes et Plans, B 1118) runs from Gibraltar almost precisely through Alexandria, whereas in reality Gibraltar shares its latitude with alexandretta (Iskenderun) about 500 km to the north, close to the point where the Levant coast turns to the west along Asia Minor.
Is there any other way such an alteration to the charts’ orientation could have plausibly occurred? Assuming – and this seems more than likely – that the earliest trial chart had already been laid down over radiating direction lines, the implementation of that change would have been simple. It is clear from surviving charts that the drafting of the compass lines [Powerpoint, Slides 8 & 15] and the hydrographic outlines was done independently from one another. It would therefore have been easy to rotate the coastlines against the north-pointing compass line if required. Once it was realised that the magnetic changes were continuous and unpredictable, and that a chart might last for a number of years, the chartmakers’ failure to track the changing position of magnetic north makes sense. If they had made adjustments, that would have led to unacceptable confusion because the user would be involved in a double calculation: first considering the ‘magnetic’ date of the chart and then having to calculate the intervening change. It would have been far easier simply to work on the understanding that, for the year they were currently in, they needed to make a particular correction to the chart’s unchanging orientation.
This one-size-fits-all re-alignment took no note of regional variation across the Mediterranean, even if mariners might have started to become aware of it by that time. However, once made, that change became permanently fixed on the charts. 141 Regional declination that resulted in different readings across the Mediterranean, as well as the progressive annual variations, were equally ignored. The close imitation enforced in the portolan chart replication process lies at the heart of their long history, and that conservativism provides a further explanation for the lack of any updating to the overall orientation.
However, we can perhaps learn, if indirectly, from the experience of later pilots. Even at the end of the 16th century, mariners were persisting with charts whose conformity with their compasses must have seemed erratic, sometimes increasingly so with the passing years. 142 It is fair to assume that they must have found a workaround. Perhaps they pragmatically rotated the compass card so as to keep it in alignment with the chart, or tested the accuracy of their needle against a sighting of Polaris.
Sticking with the 16th century, Henrique Leitão highlighted a different explanation. Even though pilots were aware of magnetic variation and declination, they did not usually correct for it. This was because the apparently erratic behaviour of the magnetic needle left pilots uncertain, and so they found it easier just to follow the uncorrected needle even though they knew that it would not point to true North. In addition, as he further points out, when a portolan chart based on uncorrected bearings was being used, it was logical to leave the compass equally uncorrected so as to match the chart. 143
The slender evidence available to us about the possibly interrelated, and perhaps contemporary, developments of the magnetic compass and portolan chart is insufficient to permit a confident account of the relationship between the two. The Carte Pisane’sAccepted as the oldest surviving portolan chart, c.1270, its author and place of origin are unknown. It has been in the Bibliothèque nationale de France since 1839 (Cartes et Plans, B 1118) magnetic tilt tells us that a compensatory adjustment had occurred by then (c.1270), but no more than that. We do not know when and how the transition between astronomical and magnetic bearings was effected. Did those who drew the early versions of the portolan chart decide to make the switch, or, far less likely, did the conjectural urchart already show that magnetic bias?
Joaquim Alves Gaspar has identified the pelagic statements in the LiberThe ’Liber de existencia riveriarum’, c.1210, written in Latin, is the oldest surviving guide to the Mediterranean, giving the distance and direction between places along the coast and across the open sea (Cotton MS Domitian A XIII, ff. 114r–129v) as a mixture of directions obtained, respectively, by astronomical and magnetic methods. The latter could be distinguished because only those reflected declination. 144 Since it is clear that a graphic medium – the putative geometric pelagic diagram on which the charts were based – could not have accommodated directions obtained from two incompatible sources, Gaspar’s suggestion that “several sources were used in the compilation of his book”, seems likely. 145
Even if the compass might not have been a pre-requisite for the chart, it could have played a major role in tightening up the geometry during the suggested ‘testing’ phase. If that is accepted, it could follow that the charts’ forerunner was based exclusively on astronomical observations, whereas by the time of the Carte Pisane the directions had become entirely magnetic, with variation treated, simply and incorrectly, as a single, uniform figure. However, the mixed message emerging from the discovery that the Liber’s list of pelagic courses includes examples of each type might imply that the transition was already under way at the beginning of the century.
The existence of memorised open-sea routes in the brains of medieval Mediterranean sailors is fundamental to the argument being expounded here, namely that the downloading of those memories provides a large part of the answer to the long-disputed issue of portolan-chart origin. Roel Nicolai’s conclusion that pelagic observations formed part of the charts’ source material can be viewed as providing at least partial support for the mental-map theory set out in this essay. 146
While much that follows in this section must, by definition, be speculative, there is a considerable amount of supporting evidence, which logically needs to be examined in some detail before considering any imagined prototype of the oldest surviving chart, the Carte PisaneAccepted as the oldest surviving portolan chart, c.1270, its author and place of origin are unknown. It has been in the Bibliothèque nationale de France since 1839 (Cartes et Plans, B 1118) . Attention will be directed in particular to the termini of the pelagic courses – i.e., the places where cargo was first shipped and where it was finally delivered. How might details about their location have been gathered?
It must first be understood that a statement in the LiberThe ’Liber de existencia riveriarum’, c.1210, written in Latin, is the oldest surviving guide to the Mediterranean, giving the distance and direction between places along the coast and across the open sea (Cotton MS Domitian A XIII, ff. 114r–129v) – for example, that to sail from Patera (in southern Asia Minor) to Alexandria (lines 762-4) involved a course of 650 milliara going due south – is not describing an actual pelagic course (even though the term per transfretum pelagi was used). What must be assumed instead is that the message it is conveying is no more than a straight-line distance, following a constant direction, between two pelagic termini. If that had been a real sailing voyage it would almost certainly have involved a number of changes of direction, because of the wind, intervening islands, etc. Furthermore, and particularly in that instance, it would often need to be different in the reverse direction.
Two 13th-century manuscript texts survive, each in a single example. They are early survivors of a type of navigation guide known as a portolan or portolano (plural portolani). The later one, Lo compasso, clearly fits that description, the oldest, the Liber only partly so. These, and particularly the Liber, have already been referred to cursorily and they will recur regularly throughout the rest of this essay. So they need introductions.
The Liber de existencia riveriarum, preserved in the British Library, (Cotton MS Domitian A XIII, ff. 114r–129v) is arranged on two-column pages spread over 16 vellum folios measuring 19.6 x 14 cm. It contains a description of the Mediterranean and Black seas by means of a listing of consecutive localities with the distances between them. In addition, and of most concern for this essay, it also includes ‘pelagic’ (open-sea) tracks with the direction and distance between the terminal points.
This important work was rediscovered and studied in detail by Patrick Gautier Dalché and published with an extensive scholarly commentary in 1995 [Powerpoint, Slide 9]. 147
[I make here a belated apology for having initially failed to appreciate the crucial importance of the Liber in this origins discussion and wish now to record my admiration for the breadth and depth of Professor Gautier Dalché’s scholarship. Modifications may need to be made to a few of his judgements in the light of fresh evidence but they will in no way diminish the fundamental importance of his Liber edition.]
Gautier Dalché had suggested a date of 1160–1200 for the Liber (p.9) but Ramon Pujades noted that the information about the Black Sea must post-date 1204, when it was opened up for trade. 147a David Jacoby went further, noting that "there is good reason to believe that the compiler of the Pisan nautical guide upon which the Pisan compiler of the Liber relied obtained information on the Black Sea from Pisans operating in that region or involved in its trade after the Latin conquest of Constantinople in 1204." On that basis, he suggests that the Liber "should be ascribed to the first three decades of the thirteenth century”. 148 No compelling evidence has yet been identified in the toponymic data to help resolve this dating uncertainty. However, a recent examination of the Liber’s section about the Black Sea has proposed c.1210 for the compilation of that text. 149
Noting that no earlier textual source has been identified, Joaquim Alves Gaspar used a new translation of the work’s ‘Prologue’ to show that “the author states clearly that he is about to describe the Mediterranean in writing and not, it is thereby understood, graphically. The likely reason for him to call attention to this detail is that the Mediterranean had already been described in a drawing.” 150 Gaspar goes on to state:
The author then gives his methodology; in order to represent those coasts on a cartula mappe mundi, he has prepared a little work (opusculum) containing the names of places with the distances between them, as well as the distances that separate Europe from Africa. For this, he has made use of data collected from mariners and travellers to supplement his own researches and studies, which had been conducted with the encouragement of a Pisan cleric critical of the way that the Mediterranean’s forma had been described in previous writings. 151
Gaspar continues: “Although the main purpose of the work, as expressed in the prologue, had nothing to do with navigation, most of its information is of a navigational nature and reflects an origin connected to maritime matters”. 152
Although the name of the Liber’s author is not known, he does leave us some clues to his identity. From his evident connections with Pisa Cathedral, and hence the likelihood that he was himself a cleric, it is not surprising to read, in the translation used by Gaspar, that he had “inserted the ancient [names] and their reason, according to the information of the books [the Bible], so that those who know the books may understand more easily”. 153 Building on that supposed identification, Pujades had suggested that “In all probability, the author of the Liber was one of the numerous clerics who acted as notaries and chaplains on the naval convoys ... Similarly, the first navigational chart makers would have belonged to this same socio-professional group”. 154
The Liber’s author claims to have traversed the Mediterranean between Alexandria and Morocco 155 and certainly some of his descriptions must have been first-hand; however, neither he nor anybody else would have sailed systematically round the Mediterranean (and Black Sea) in order to put together such a handbook. Hence, he acknowledges the information provided to him, by “mariners and travellers”. 156 That mixture of experience and report is also reflected in the phrases he uses: “I have been able to know and discover”; “as I have seen and travelled”; “on the basis of calculation”; “that I could learn”. 157 Certainly more than just literacy was needed by the (apparently) first compiler of such a maritime guide. He must have had a methodical mind allied to a coherent plan for achieving a complete or at least broad coverage.
The second text in the spotlight, Lo compasso de navegare, is preserved in the Staatsbibliothek, Berlin (MS Hamilton 396), and is laid out on 107 vellum folios, measuring 21 x 14 cm. Considerably more detailed than the Liber, it likewise covers the Mediterranean and Black seas but has a full coverage of the latter compared to the Liber’s sparse toponymy. Lo compasso provides more precise bearings between neighbouring coastal localities than the Liber and includes many times as many ‘pelagic’ (open-sea) tracks.
The surviving manuscript has the stated date of 1296, but contradictory suggestions have been made: that the extant text may be both a revision of an earlier version around 1260 and at the same time a 14th-century copy, perhaps from as late as the 1320s. 158 The work’s first editor, Bacchisio Motzo (1947), had proposed that the surviving text of Lo compasso is an updated version of a work composed in the mid-13th century (probably before 1256 since it does not include Manfredonia, founded in that year); this is not disputed by its most recent editor, Alessandra Debanne (2011) [Powerpoint, Slide 10]. Pujades pointed out that its text refers to Palamos, founded by Peter II of Aragon in 1279, which would move forward the earliest possible date. 159 However, as Debanne notes, the description for Brindisi does not mention significant changes to its harbour that took place in 1276, which would imply a date prior to that. 160
In a review article, Andrea Bocchi suggests that the stated date of the surviving manuscript should probably be read as January 1295 not 1296, which would have bearing on the noted absence of Villefranche, founded in 1295 on the site of Olivoli. 161 He also found evidence of scribal confusion that could indicate later interpolations. While these different indications warn against confident dating statements, it seems likely that the original version of Lo compasso was created at some point around the mid-13th century and that additions – although nobody has yet identified which those might be – were introduced up to and perhaps beyond 1295.
It needs to be emphasised that there is little similarity between the two portolani. That Lo compasso is not an imitation of the Liber is underscored by their itineraries proceeding in opposite directions. 162 The Liber’s author had ecclesiastical connections and, as he states, part of his motivation was to foster what might be termed biblical tourism. In contrast, Lo compasso should be considered as probably the oldest (and certainly the fullest) example of a true portolano: a descriptive itinerary around the Mediterranean’s periphery and between its islands. Navigation was central to the work’s concern and it appears have been aimed at mariners, providing basic information that would help them to navigate safely. To that end, it offers short evaluative and descriptive comments about entering a harbour, nearby navigational hazards, the appearance of the coastline, and so on. 163
We owe our knowledge of these two unique manuscripts to the scholars who identified and interpreted them, without which there would be no textual material from before the likely date of the Carte PisaneAccepted as the oldest surviving portolan chart, c.1270, its author and place of origin are unknown. It has been in the Bibliothèque nationale de France since 1839 (Cartes et Plans, B 1118) . Those documents are crucial witnesses to the charts’ prehistory.
We cannot rule out that the oldest survivor of the genre, the Liber, The ’Liber de existencia riveriarum’, c.1210, written in Latin, is the oldest surviving guide to the Mediterranean, giving the distance and direction between places along the coast and across the open sea (Cotton MS Domitian A XIII, ff. 114r–129v) might have had antecedents (although its first-person narrative might argue against that). However, even if there are lost predecessors, the central question remains, where would their navigational information have come from: previous – even ancient – texts, or, as is argued here, sailors’ memories? Danny Lee Davis poses the same question about mental map or text in the Classical world, without being able to give a definitive answer:
From these observations and general conclusions are we to gather that seafarers completely shunned written aids and instead relied on their cognitive abilities alone to store and call up the important navigational information they learned from experience? Or did they use written materials that simply have not survived in any form. 164
The improbability that such a precursor text ever existed can be best demonstrated by contrasting the likely content of such a hypothetical document with what was required for navigation. Lo compasso’Lo compasso de navegare’, c.1260-96, written in Italian and apparently designed for sailors, is much more detailed than the earlier ’Liber’ (Staatsbibliothek, Berlin, MS Hamilton 396) was at least partly aimed at mariners, since it contains impressively detailed information for use by cabotage sailors. But what had appeared to be pelagic instructions for the open-sea transits have turned out to be no more than measurements from a chart. As Peregrine Horden and Nicholas Purcell emphasize, “the myriad possible combinations of port, shelter, detour and accident comprised by even short journeys could hardly be mapped or set in writing”. 165
If instead we look in the other direction, at later portolani (Singular portolano and more usually called ‘portolans’ – which can be confused with the charts) these were medieval guides to the coastal places around the Mediterranean, listing the distances between them. They also include open-sea (pelagic) routes – in case archaic elements were resurrected there – we find a continuation over several centuries of what are primarily lists of distances and directions, mostly involving adjacent coastal points. Little extraneous information was added, apart from depth figures, such as those in Grazioso Benincasa An ex-ship captain, he left us a range of clearly-drawn charts and atlases (1461-82) and a written portolano (1435-45)’s portolano of 1435–45. 166
At no stage did the pilot books introduce detailed sailing notes; even in the 16th century when printing would have made it easier to circulate information of that type. If 14th-, or more particularly 15th-century portolani, which survive in significant numbers, had included information that was clearly directed at mariners, there might have been some justification for claiming that those details could have existed prior to Lo compasso. But that was not the case. As for sailing directions as generally understood, these only appeared, in printed form, in fairly recent times and, rather than relying on written description alone, they supplied recognition views of coastal profiles.
That is not to deny that, in the Islamic world, written sailing directions, of some kind, do indeed pre-date the portolan chart. We learn, for example, from the 11th-century Book of CuriositiesAn Arabic manuscript of the 11th century including maps and descriptions of the Mediterranean, but not related to the portolan chart – see Section A.3a, and Rapoport & Savage-Smith, 2018 that its nautical information had been provided by “sailors, merchants and ships’ captains”. Furthermore, from a 10th-century Islamic source, al-Muqaddasi, it appears that, for the Indian Ocean at least, sailors followed instructions in unillustrated ledgers. 167 Tarek Kahlaoui describes how the text accompanying al-Idrīsī’s large world map provided a wide range of information from mariners, among which was “a list of sites, with the distances between them and their neighboring coastal sites”, along with “notes about the kind of goods (food and water) available at each location” as well as “tools to aid in the visualization of the outline of the coastline.” 168
Hence, in the Islamic world at least, texts were certainly provided for use by mariners. But, crucially, this seems to have involved coastal sailing only, not the more challenging pelagic courses. Nor were those Arabic sailing directions imitated in the Christian West.
The authors of the ground-breaking study of The Book of Curiosities conclude, in words that have strong echoes for the primacy of the early portolan charts over text, that the author of that work “has unprecedented confidence in the ability of maps and diagrams to convey information. Unlike any other geographical treatise before this, the maps are stand-alone artifacts, unsupported by any accompanying text”. 169
Furthermore, the very limited practical use of the written portolano for navigation 170 – confirmed by the lack of their presence alongside portolan charts in the inventories of sailors who died abroad 171 – makes it unlikely that most 13th-century sailors would even have been aware of their existence, let alone have used them, or probably been able to read them anyway. Not only can the use of pilot-books at sea be questioned, but there does not seem to be any trace of early logs of individual voyages written by mariners rather than passengers. That convention may perhaps have started with the voyages of discovery in the 15th or 16th century, becoming thereafter a routine requirement on long voyages, especially to the East.
There is no reason to suppose that medieval mariners would have had the equivalent of a trade manual, or indeed that any specialist craft at that time would have been supplied with written instructions. Nor was apprenticeship focused on book learning, since most artisanal skills were learnt through imitation and oral instruction alone. 172
Three specific arguments against conjectural antecedents to the surviving portolani would be these:
We need to avoid the anachronism of trying to insert into the medieval period the content of much later navigational guides. 174
The pelagic courses tend to be interspersed throughout the LiberThe ’Liber de existencia riveriarum’, c.1210, written in Latin, is the oldest surviving guide to the Mediterranean, giving the distance and direction between places along the coast and across the open sea (Cotton MS Domitian A XIII, ff. 114r–129v), whereas in Lo compasso’Lo compasso de navegare’, c.1260-96, written in Italian and apparently designed for sailors, is much more detailed than the earlier ’Liber’ (Staatsbibliothek, Berlin, MS Hamilton 396) they are either included in the general narrative or given their own ‘Peleio’ sections. Such courses usually, but not always, cover a considerable distance. Their essential characteristic is that they involve the ship setting out to sea, rather than just following the coast. In some instances, the journeys would be short enough to involve land that was always in sight, such as an offshore island. The network of courses mentioned in the Liber have been drawn out in the form of a diagram by the work’s editor, placed at the end of the volume. A necessarily more elaborate equivalent has been provided by Roel Nicolai for the far more extensive network described in Lo compasso . 175
The pelagic statements are presented in forms like these:
'Liber': a Maluascia ad caput Malee Sancti Angeli inter eurum et austrum ml. .xx [From Monemvasia to cape Malée following a direction between south-east and south, 20 miles]
'Lo compasso': Acque morte all’isola de San Piero CCCCLXXXX millara per sirocco ver lo meczo di poco [Aigues-Mortes to Isle S. Piero, 490 miles following a direction between south-east and a little towards south] 176
Unsurprisingly, the pelagic termini mentioned in those two early portolani include headlands, islands, commercially prominent ports, and occasionally mountains close to shore. 177 Promontories feature strongly among the termini. They were broadly of two types. First, those projecting out from the coast and therefore useful for marking the progress of a voyage. Second, a cape (whether on the mainland or protruding from an island) that indicated a change in the direction of the coast. A helmsman would have aimed for one of those after it had been sighted and recognised. He would then use it to re-align his bearing for the next stage of the voyage. Some of those capes and islands represented crucial turning-points. Good instances are Cape St Vincent which marks the point where ships turn towards the east for the entrance to the Mediterranean, and those that mark out the broad overall shape of Italy’s foot, Spartivento and Santa Maria di Leuca. As is argued below 178 they could also have provided the key locations used to construct a tightly interlinked network of direction lines and nodal points to form the geometric outline of a portolan chart.
Islands, both large and small, played a major role in Mediterranean navigation. Whether or not they were visited, they could serve as intermediate destinations. As might be expected, many of the islands’ outer promontories are named in the list of pelagic courses. 179
Besides the main body of the Liber, which comprises a coastal itinerary linking one port or feature to the next, there are three additional summary lists: