It’s a mistake to think, since they thought the sun and planets revolved around the earth, therefore medieval men were egocentric fools. It’s not so much they thought the earth was at the center, but that they thought it was at the bottom.
UPDATE 25 August 2011:
“What we call gravitation–for the medievals ‘kindly enclyning’–was a matter of common knowledge. Vincent of Beauvais expounds it by asking what would happen if there were a hole bored through the globe of Earth so that there was a free passage from the one sky to the other, and someone dropped a stone down it. He answers that it would come to rest at the centre.” — C.S. Lewis, The Discarded Image, Flat-earthers, and ‘kindly enclyning’