Article ID: CBB832686811

The Accuracy of Ancient Cartography Reassessed: The Longitude Error in Ptolemy’s Map (2016)

unapi

This essay seeks to explain the most glaring error in Ptolemy’s geography: the greatly exaggerated longitudinal extent of the known world as shown on his map. The main focus is on a recent hypothesis that attributes all responsibility for this error to Ptolemy’s adoption of the wrong value for the circumference of the Earth. This explanation has challenging implications for our understanding of ancient geography: it presupposes that before Ptolemy there had been a tradition of high-accuracy geodesy and cartography based on Eratosthenes’ measurement of the Earth. The essay argues that this hypothesis does not stand up to scrutiny. The story proves to be much more complex than can be accounted for by a single-factor explanation. A more careful analysis of the evidence allows us to assess the individual contribution to Ptolemy’s error made by each character in this story: Eratosthenes, Ptolemy, ancient surveyors, and others. As a result, a more balanced and well-founded assessment is offered: Ptolemy’s reputation is rehabilitated in part, and the delusion of high-accuracy ancient cartography is dispelled.

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Authors & Contributors
Prontera, Francesco
Seubert, Philippe
Haushalter, Arthur
Panichi, Silvia
Ilyushechkina, Ekaterina
Janni, Pietro
Concepts
Geography
Cartography
Roman Empire
Longitude and latitude
Geographers
Cartographers
Time Periods
Ancient
Medieval
Places
Rome (Italy)
Mediterranean region
Greece
Middle and Near East
Europe
Arabian peninsula
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