Eratosthenes’ Contribution to Ptolemy’s Map of the World

Abstract

ABSTRACTThis article attempts to shed some light on the origins of Ptolemy’s map of the world, which remains a mystery. The premise is that Ptolemy and other ancient geographers largely drew on the same or a similar pool of sources and common beliefs. Similarities between them can, therefore, give us a key to understanding the prehistory of Ptolemy’s map. Comparison of distances on his map with those given by other sources leads to the conclusion that a large area of the map, approximately from the Bosporus to the Indus, reproduced Eratosthenes’ geographical system, with linear distances converted to angular degrees according to Eratosthenes’ own scale. It is argued that this area represents a remnant of an earlier version of Ptolemy’s map. Analysis of latitude and longitude reveals notable differences between Ptolemy’s map and Eratosthenes’ ideas concerning the latitude of Babylon and the Alexandrian prime meridian, and the impact this seems to have had on the shape of neighbouring regions is noted.