What is the shape and size of the Earth? This lecture traces historical ideas about the shape of the Earth, from ancient ideas of a Flat-Earth to Aristotle's compelling demonstrations in the 3rd century BC that the Earth was a sphere. We then discuss two famous classical measurements of the circumference of the Earth by Eratosthenes of Cyrene in the 3rd century BC and Claudius Ptolemy in the 2nd century AD. Recorded 2007 Sep 24 in 1000 McPherson Lab on the Columbus campus of The Ohio State University.