Medieval sea-charts - centuries before their time

Figure 1: Annotating portolan charts in Recogito

It's hard to describe the appearance of a portolan chart - the medieval answer to the modern Admiralty chart - if you haven't already been able to see one.  Very few early examples are freely available online but you can find a chart of 1403 here: http://brbl-dl.library.yale.edu/vufind/Record/3521236. Probably originating in the 13th century, though not everybody agrees about that, the portolan charts present the Old World with immediate recognisability.  Covering the coastlines of the Mediterranean and Black Seas, along with the Atlantic shoreline up to Denmark (and the British Isles), they contradict every normal preconception about medieval cartography. You don't need to have Italy, the Nile delta, Crimea and so on pointed out.  They are where you would expect and pretty much how they ought to be.

Why Pelagios 3 devotes an entire segment to the 'portolan' world though is because of their dense toponymy. Taking into account all the islands, an average chart lists perhaps 2000 ports and harbours, as well as natural features, especially the headlands which served as reference points for sailors.

Besides the portolan charts we also have access to portolan texts or, to help distinguish the two formats, the Italian term, portolano / portolani.  Two of those survive from the 13th century, also the likely date (at its very end) of the Carte Pisane that is generally considered the oldest extant chart.  Whereas the delineation of the coastlines had, by about 1340, broadly reached the form that would be repeated for several centuries, the place-names were being steadily updated.  Given the Pelagios terminal date of 1492, that gives us a changing toponymy from three centuries of written navigational guides and two in the case of the charts.

The portolan component will both enrich Pelagios and, we hope, benefit from it. Less than half the coastal toponyms on the oldest portolani, the 'Liber de existencia riveriarum' (early 13th century) and 'Lo compasso de navegare' (dated 1296), are found on the other, and a sizeable number do not appear on the charts at all.  Likewise the toponymy of the Carte Pisane, and two other anonymous charts associated with it  (now preserved in Cortona and Lucca) partly overlap with one another but also have hundreds of names not seen elsewhere.  Considered together, these are rich sources for historians of medieval navigation and trade, since their inclusion in these works must point to them having a perceived significance at the time - even more so for the roughly one in five names that were picked out in red on the charts.

Overall, and leaving aside the islands, there are about 2000 mainland names that can be tied to a dated chart or atlas before 1492 and something like a further 600 noted only in one or other of the portolani texts or undated charts.  Conveniently, both the portolani narratives and the nautical charts provide a geographically linear toponymic catalogue for the Mediterranean and Black Sea. When the current name can be recognised in its medieval equivalent, or where the successive re-naming has been documented, those fixed points can then be used to locate the approximate present-day position of unidentified names. The most helpful source for this matching exercise will be 19th and 20th-century maps and Admiralty charts produced before expanding ports, or the general touristification of the sandy bits in between, gobbled up the old names, and often what they represented as well.  Early gazetteers can help to corroborate the guesswork.

That describes the potential contribution that the rich maritime data can make to Pelagios.  In exchange, portolan historians anticipate the help that other medieval maps and texts can give with the modern identification of some of the more elusive toponyms they have been wrestling with.  Regional historians and archaeologists may also appreciate being introduced to what will be a new source to many of them.

The toponymy for some of the portolan regions have already been documented in detail (N.E. Spain, the Adriatic and the Black Sea). Besides what is being extracted from the original documents by the Pelagios team, the remainder will be sourced from a comprehensive listing that was compiled originally in preparation for a chapter in Volume 1 of The History of  Cartography (University of Chicago Press, 1987) and then fleshed out and expanded over recent years.  The resulting Excel spreadsheet is publicly accessible at http://www.maphistory.info/PortolanChartToponymyFullTableREVISED.xls, where it forms part of a detailed ongoing investigation into the portolan charts (http://www.maphistory.info/portolan.html).

**Former map librarian of the British Library (1987-2001), since 1993 Tony Campbell has been chairman of Imago Mundi Ltd, in which capacity he acts as co-ordinator for the biennial International Conference on the History of Cartography. He is working on Pelagios 4 as the expert adviser on portolan charts.