Philosophers. Ignorance of the landscape did not come about for the Romans from lack of trying. Travelers of all varieties—generals, merchants, tourists, and so forth— studied the geographic texts and theories that were available to them from Hellenistic scholars. Most of these earlier philosophers at least had realized that the world was round; Eratosthenes even calculated the length of the equator; his estimate of 252,000 stades (approximately 27,967 miles) is a little over the true measurement (24,902 miles), despite his complete ignorance of the Americas. Many of the Hellenistic geographers also believed that their plot of inhabited land was surrounded by a great ocean on all sides; technically correct if one thinks only of the three continents —Europe, Africa, and Asia—that each branch off from the central Mediterranean (central, that is, to their understanding). One influential account in particular was...