Dear plutarch: Long before Magellan, the Greeks knew the earth was round, and even computed its circumference:
Eratosthenes made a surprisingly accurate measurement of the circumference of the Earth. Details were given in his treatise On
the measurement of the Earth which is now lost. However, some details of these calculations appear in works by other authors such as Cleomedes, Theon of Smyrna and Strabo. Eratosthenes compared the noon shadow at midsummer between Syene (now Aswan on the Nile in Egypt) and Alexandria. He assumed that the sun was so far away that its rays were essentially parallel, and then with a knowledge of the distance between Syene and Alexandria, he gave the length of the circumference of the Earth as 250,000 stadia.
There is now some disagreement about the length of the stadium, but it does not really diminish his feat.
