Geography

Ptolemy believed the earth was round, which, perhaps surprisingly, wasn’t a new idea even in the second century. Aristotle had argued that the earth was round five centuries earlier. Eratosthenes devised a clever geometric experiment to actually measure the earth’s diameter, and did so four centuries before the Almagest was written. A round earth played an important role in Ptolemy’s other well known work, the Geographia. In the Almagest, Ptolemy laid out a map of the heavens. In the Geographia, he laid out a map of the earth.

 

Ptolemy's Geographia is known also as the 5th map of the Earth in history. So it's easy to find problems with the accuracy and land masses of the map. But what really stands out in Ptolemy’s world map are the beautiful, gently curving lines of latitude — a clear, visual reminder that we live on the surface of a ball, and that we’ve known it for thousands of years.