The configuration of the Pontus Euxinus in Ptolemy's <i>Geography</i>

Abstract

This article aims to explain how Ptolemy could have constructed a map of the Pontus Euxinus (Black Sea), as described in his Geography, under the assumption that his sources were similar to those that have come down to us. The method employed is based on the comparison of Ptolemy's data with corresponding information from other ancient sources, revealing the most conspicuous similarities and differences between them. Three types of information are considered as possible “constituent elements” of Ptolemy's map: latitudes, coastline lengths, and straight-line distances. It is argued that the latitudes Ptolemy used for the key points determining the overall shape of the Pontus (Byzantium, Trapezus, the mouth of the Borysthenes and the Cimmerian Bosporus, the mouth of the Tanais, etc.) were most likely inherited from earlier geographers (Eratosthenes, Hipparchus, and Marinus). In exactly the same way, Ptolemy's data on the circumference of the Pontus and the length of the coastal stretches between the key points (from the Thracian Bosporus to Cape Karambis, Sinope, Trapezus, and the mouth of the Phasis, etc.) closely correlate with the corresponding estimates reported by other geographers (Eratosthenes, Artemidorus, Strabo, Pliny, Arrian, and Pseudo-Arrian), which implies that Ptolemy drew on similar coastline length information. The shortening of Ptolemy's west coast of the Pontus (from the Thracian Bosporus to the mouth of the Borysthenes) relative to the corresponding distances reported by other sources is explained by his underestimation of the circumference of the Earth. The lengthening of Ptolemy's north-east Pontus coast (from the Cimmerian Bosporus to the mouth of the Phasis) can, in part, be accounted for by his attempt to incorporate the straight-line distances across the open sea reported by Pliny. Overall, Ptolemy's configuration of the Black Sea can be satisfactorily explained as a result of fitting contradictory pieces of information together that were inherited from earlier geographical traditions.