Sarita Armstrong

The Jehudi Ibn Ben Zara Portolan

Anyone who has taken a holiday on the Greek island of Kos and sat on the town beach gazing out to sea with nothing better to do, may have wondered why the large cruise liners and Greek ferry boats make a long detour round apparently empty sea before turning into the port of Kos. Even small sailing boats leaving harbour make the long tack towards Turkey before turning north or west.

The reason is really quite simple. They are all avoiding a long underwater shelf that sticks out like a finger from the north-east corner of the island. Nothing special about that, you may think. But what is interesting is that a medieval portolan map of the area drawn by an Alexandrian cartographer by the name of Jehudi Ibn Ben Zara in 1487 shows this geological formation as part of the island, clearly above water.

Was this underwater shelf above water in 1487 or was the cartographer describing land as it was in an earlier time? The latter seems more likely, for it is not the only island this cartographer shows in a form altered from how we see them today. For one thing, all the Aegean islands appear to be larger. The island of Rhodes is much wider – extended on the eastern side. Crete is wider north to south. With our superior knowledge we simply say: he got it wrong. But did he? Or is this interesting fact telling us something quite different?

 Hapgood (1), Nordenskiöld (11) and others who have made a study of the medieval portolans considered they were showing information from much earlier work that is now lost. Hapgood also writes: “I had been attracted to the study of this portolano because it seemed definitely superior to all the other portolan charts I had seen in the fineness of its delineation of the detail of the coasts. As I examined these details in comparison with the modern maps, I was amazed that no islet, no matter how small, seemed too small to be noted”

The shape that is drawn frequently follows the 50 metre underwater contour on today’s charts. We find it hard to believe that the sea was that much lower in the 15th century, but another interesting point is that the Ibn Ben Zara portolan shows information prior to the eruption of the Thera volcano on the Aegean island of Santorini. (See Figure 1 in The Odysseus Code).

The Thera volcano erupted around 1500 BC after which seafaring in the Mediterranean declined. Jehudi Ibn Ben Zara was taking information from maps that were gathered together as antiquities in the Library of Alexandria – maps that must have been in circulation amongst seafarers of a much earlier period, of which perhaps the Phoenicians and Minoans were the last survivors.

No cartographer visits all the places on his charts to verify their exactitude, but makes copies from older charts and upgrades them from information given to him by recent seafarers. This happens even today when many sailors are happily using charts first drawn in the 19th century and revised only by sailors’ reported information. It was no different for Ibn Ben Zara, except that for centuries after the Thera volcano erupted nobody was sailing about very much and certainly they were not sending their reports back to a centralised location like Alexandria. Four times larger than Krakatoa, the Thera eruption was no huff and puff – it blew the whole island apart.

There is a whole area of ancient geography and history unexplored in the portolans generally. We have always assumed that if something is not as we see today it must therefore be an error on the part of the historical writer, but we have limited our horizons by taking this attitude. Perhaps it is time to take another look.




 1    Charles H. Hapgood, FRGS, Maps of the Ancient Sea Kings Philadelphia (N.Y.) Chilton Books 1966

 11  Baron Adolf Erik Nordenskiöld was a Finnish explorer born in 1832, exiled to Sweden.  His collection of ancient cartography and many other works in Helsinki University Library including 24,000 historical maps is considered by UNESCO to be one of the world's most important collections of documents.