The Black Sea in Ptolemy’s Geography: from measuring latitudes and distances to creating a map

The configuration of the Black Sea in Ptolemy’s Geography is compared with the information of other ancient geographers. It is demonstrated that their data on the length of the coastlines between the key points match with high accuracy, implying that they drew on similar sources. A possible explanation of numerous disagreements between their data on distances between neighbouring coastal points is suggested. It is shown that the shortening of the west coast of the Black Sea in Ptolemy’s Geography relative to the reports of other geographers was due to his erroneous value of the circumference of the Earth. In general, Ptolemy’s configuration of the Black Sea is explained as a result of merging together contradictory information on the length of coastlines and the latitudes of the key points provided by his sources. These findings contribute to a better understanding of Ptolemy’s method of map-making.