[Locke1689]

Actually, that entire story is a myth invented in modern times to paint ancient thinkers as "backwards." And I quote:

The myth that people in the Middle Ages thought the earth is flat appears to date from the 17th century as part of the campaign by Protestants against Catholic teaching. But it gained currency in the 19th century, thanks to inaccurate histories such as John William Draper's History of the Conflict Between Religion and Science (1874) and Andrew Dickson White's History of the Warfare of Science with Theology in Christendom (1896).