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Ptolemy's World

On Mapmaking

The Indian Ocean--Enclosed or Open?

Ptolemy’s text concludes with "A descriptive summary of the map of the inhabited earth" and the statement: "That part of the earth which is inhabited by us is bounded on the east by the unknown land which borders on the eastern races of Greater Asia, namely the Sinae and the Seres, and on the south by the likewise unknown land which encloses the Indian sea and which encompasses Ethiopia south of Libya, the country called Agisymba, and on the west by the unknown land encircling the Ethiopian gulf of Libya and by the Western ocean bordering on the western-most parts of Africa and Europe. . . ." (Ptolemy 1932, 159). This statement, if it is indeed that of Ptolemy, states the belief that the Indian Ocean was enclosed by land stretching from southern Africa all the way to eastern Asia.


This assumption has been debated. Wilcomb Washburn, in an article published in 1985, argued that Ptolemy and other geographers of his time and earlier did not believe in the closed Indian Ocean. Instead, according to Washburn, this idea emerged in the late Middle Ages in relation to arguments between those who believed that the unknown portions of the earth were primarily land versus those who believed that the unknown regions were predominantly seas. Washburn wrote that the "arbitrary character of the presumed southern border of the map and the southern border of the land on Ptolemy’s maps" suggests errors of copyists. Though he had never made an actual count, Washburn thought that most of the printed editions of Ptolemy’s Geographia showed the enclosed Indian Ocean while many of the manuscript world maps had an open Indian Ocean. The areas in question should have been left as blanks if the mapmakers were being honest, but because of "man’s compulsion to fill them in" the land bridge was added (Washburn 1985, 437). One radical interpretation of the "enclosed" sea is worth noting. D.E. Ibarra Grasso, in 1970, proposed the thesis that the enclosed sea is the Pacific Ocean. In that case Cattigara is on the west coast of South America. This idea has not received much support, as it would be very difficult to prove, but it is a stimulating idea in any case, and one example of how different viewers may interpret maps in various ways (Dilke 1987, 199).