Christopher Columbus did not believe the world was flat.

In fact, nearly no educated person has held this belief since the time of the ancient Greeks! The idea of a spherical Earth first appeared around the 6th century B.C. with the Greek mathematician Pythagoras and continued to permeate Greek and Roman culture, even after the advent of Christianity. The thought that Columbus held such a fallacy did not emerge until the 1830’s, when a Frenchman named Antoine-Jean Letronne and the well-known American author Washington Irving separately composed works of historical fiction which misrepresented Columbus. This myth eventually made its way into schoolbooks and is still often taught to this day! The lie is believed to have been promoted as a way of heightening the religion/science debate and giving ammunition to Darwinism over creationism.

Source: ASA