Why Were Medieval Sea Charts Still Being Produced Four Centuries Later? Does the Answer Lie in the Aegean?
Portolan charts have been studied for more than a century and a half, and intensively so in recent years. Yet several basic questions remain unanswered; indeed, some have never been asked. Publication of a major study by Ramon Pujades in 2007 was accompanied by a DVD with scans of all the charts up to 1469. For the first time it became possible to carry out a comprehensive analysis of the widely spread, and mostly un-reproduced, early charts. An investigation over the last few years, spurred on by that initiative, focused among other elements on the place-names, and the shapes of the medium and small islands. Those detailed findings have made it possible to propose answers to fundamental questions relating to the purpose and longevity of the medieval sea charts.
Portolan charts contain an unexpected mixture of surprising geometric accuracy and apparently frivolous invention. Their toponymy was static enough to include in 1600 three-quarters of the names that can be seen 300 years earlier. Yet at the same time they were dynamic enough to introduce many hundreds of new, and subsequently repeated, names over that period, and to jettison hundreds of others.
It will be demonstrated that the portolan charts - leaving aside their land-based roles as decorative or prestige objects - were an essential tool for sailors. Their uneven 'accuracy' can be explained in terms of three distinct seaboard uses: first, when on a long sea passage out of sight of land, second, when working from headland to headland along a coast, and third, when picking a way through an archipelago - particularly those in the Aegean Sea.
It is ironical that their continued relevance for merchant shipping can be attributed to the reverence with which every small hydrographical detail of the original workshop model was faithfully copied through perhaps eight generations, and not to their adaptability in the face of what we might have supposed were evolutionary pressures. Only the vital, and ever-changing toponymy contradicts that statement.