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behind the essay

'Mediterranean portolan charts: their origin in the mental maps of medieval sailors,
their function and their early development'


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Genesis of this essay

When I submitted an overview of the early portolan charts for the first volume of The History of Cartography (published in 1987), I avoided the ‘origin’ question, assuming that to be largely a question of mathematics, of which I had (and still have) insufficient command. I fully appreciated that left a gap and was very grateful to David Woodward for stepping in to fill that lacuna (pp. 387-8).

The publication of Roel Nicolai’s doctoral thesis (The Enigma of the Origin of Portolan Charts. A Geodetic Analysis of the Origin of Portolan Charts (Leiden; Boston: Brill, 2016)) brought me back to the origin question because, despite the thoroughness of that cartometric analysis, the final conclusion was that the charts’ unprecedentedly realistic outlines would have been beyond the capabilities of medieval navigators and must therefore have been inherited from an earlier culture. That lack of a plausible historical explanation for the charts’ origin identified a space that needed to be filled. The result, this essay, is of comparable length to that earlier synthesis of the first two centuries of the portolan charts. By contrast, this deals with what at first had seemed to be a narrower focus on the navigational abilities, practices and requirements of sea-going sailors around 1200, with the aim of providing a coherent historical solution that could embrace all aspects of that complex question. In the event, this study took four years.

In 2007, portolan-chart historians were provided with a magnificent resource denied to their predecessors, in the form of a DVD accompanying Ramon Pujades’s massive survey, Les cartes portolanes: la representació medieval d'una mar solcada ). That contained rotatable scans of almost all the charts and atlases produced up to 1469, which can also be enlarged beyond the size of the original. As a result, the toponymy is, in most cases, fully legible.

For the origin question, the most useful images are those of the Carte Pisane (c.1270) and the first charts that followed afterwards, since those must contain part of the DNA of the lost antecedents, going back perhaps to the end of the 12th century. [Because they were discovered only recently, the DVD does not include the Avignon or Lucca charts.]

My long essay on the Carte Pisane, published in 2015, assisted in establishing the background. As did a suite of analytical studies, made possible by the Pujades DVD, published from 2011 onwards. Much of the focus was on toponymy, revealing both general patterns and idiosyncrasies. Despite the continuous addition of new place-names, one of the findings was that the average time-lag between the naming of a place and its appearance on a chart was 75 years – a necessary corrective to the assumption that portolan charts would generally be up to date. Other topics were investigated as well, among them the wide range of innovations introduced on the charts, the handling of the colour and shapes of islands, and workshop practice. These studies can all be found on the ‘Map History’ site, in the Portolan Chart section, or via the Portolan Chart Bibliography. Most of the factual information about the portolan charts in this essay comes from those studies.


Assumptions and speculations

In the absence of hard facts speculation is sometimes unavoidable. However, assumptions on which arguments are then to be built need to be carefully considered and openly stated; if the hypothesis is overturned then the whole edifice could fall.

It has to be acknowledged that, in the search for the portolan chart origins – which has had many ‘solutions’ over the years, none of which commands general respect today – there is, quite simply, no documentary evidence. The lack of contemporary references is disappointing, with virtually no medieval writers being identified as having commented on the portolan charts. That is not so surprising; since the charts were produced in various Mediterranean ports for the use of seamen, their overlap with the literary and administrative worlds would have been slight. Hence the scarce texts that do refer to them are much valued.

The main source available to us is Patrick Gautier Dalché’s edition of the Liber de existencia riveriarum et forma maris nostri Mediterranei (1995). Dating probably from the very beginning of the 13th century and hence close to the time that the urchart was likely to have emerged, this gives us no more than oblique hints, some of which invite alternative meanings.

So, an investigation into the origins question has to start with a working hypothesis of some kind. In this case the assumptions underpinning the whole essay, and perhaps better described as assertions, can be stated simply thus:

  1. No mariner would routinely have left port without knowing the direction to take and the approximate distance and time involved to reach the planned destination
  2. 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
  3. Details of pelagic courses in the Mediterranean must have been held in sailors’ memories for millennia, hence a 12th-century pilot would have been using some kind of mental map
  4. Whenever information is vital, there is a strong incentive to commit it to memory
  5. The charts’ geometry could plausibly have come from one source only: pelagic courses memorised by pilots
  6. There can be no discussion of the portolan charts’ origin and use without considering them as objects of commerce

In recent discussions with others, seeking answers to the same ‘Origins’ questions, alternative assumptions seem to have been made, for example that:

These issues are discussed fully in the essay, and each is strongly challenged in detail, but the essential point is that an attempt was made here to avoid starting the examination of portolan-chart history with unsupported assumptions, since those would have automatically ruled out other alternatives. Whether I have succeeded is up to others to judge.

In two cases I have intentionally broken that self-imposed rule. The first reflects 20 years’ experience in a commercial environment which meant it did not seem unreasonable to assume that portolan chartmakers over some four centuries had worked not for love, but to put food on the table. I cannot see how the portolan chart can be studied without seeing it, above all else, as a commercial production, where the needs of producers and users had to be balanced.

The second falling away from pure objectivity is a decision, when evidence is absent, to favour what seems logical and plausible, in other words whatever matches what we know about human nature, and to reject whatever does not. Others are entitled to feel that, in the process, I may have taken liberties with expected medieval practices.


Questions posed

Answers often depend on the way the questions are posed. The numerous insights (if so they be) that appear here in this essay for the first time stem from a process that involved digging ever deeper, well beyond where others had stopped. My contention is that the charts’ origin has been overlooked largely because it did not have textual sources but rather depended on memorised information and oral transmission, neither of which would leave any trace. Like an astronomer realising what must be there, even when it could not be seen, this study had to abandon traditional, orthodox approaches to cartographic history, and indeed all precedents, before it was possible to see the solutions I am proposing. The portolan chart was revolutionary, and in many ways. Perhaps it needed an unorthodox approach to reveal its secrets. The unfamiliar is not the same as the improbable. “If our attention is focused on only what we expect to see, we will miss the unexpected” (Christopher Clarkson, ‘Rediscovering parchment: the nature of the beast‘, in: Nicholas Hadgraft & Katherine Swift (eds) Conservation and preservation in small libraries (Cambridge, Corpus Christi College, Parker Library Publications, 1994) p.76).


Hypotheses tested

To hope to understand the portolan chart we have to attempt to enter the mind of a medieval pilot. Of course that is only partly possible (even for a modern navigator) but it can eliminate some hypotheses, for example the anachronistic idea of a systematic coastal survey. Given that the aids available to those sailing in the Mediterranean changed little between the Bronze Age and the relatively recent past, we do, though, have access to a considerable amount of information about comparable navigating techniques, whether historical or from indigenous communities.

It is fair to assume that medieval mariners would have needed well-developed navigation skills for their own survival, aided by senses far more attuned to their surroundings than those thought necessary today. Nor can there be any doubt, in the face of constant, often mortal danger, that professional pilots would have gladly taken advantage of any device – be it a magnetic compass or a portolan chart – if it might lessen those risks.

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