When did people stop believing the world was flat?

Answer 1

A lot of them haven't. The ancient Greeks knew that the world was not flat, they didn't all believe it was round, some thought it a kind of circular spiral, but that knowledge was lost during the Dark Ages. By 1500, many educated people believed that the world was round, but it was not until the 1800's that that knowledge became widespread. this is mainly due to people who went against the beliefs of the time, generally got themselves killed. It is possible that the ancient Hebrews always knew that the world was round: Isaiah 40:22 says "he sits enthroned above the circle of the earth"