Did medieval people really think the Earth was flat?

The widespread belief that medieval Europeans thought the world was flat is itself a myth, and a fairly modern one. Educated people knew the Earth was spherical for more than two thousand years. The ancient Greeks established it: Pythagoras proposed it, Aristotle gave observational proof (ships disappearing hull-first over the horizon, the round shadow on the moon during eclipses), and around 240 BC Eratosthenes calculated the Earth's circumference with remarkable accuracy using shadows and geometry. That knowledge was preserved through the medieval period; scholars, the Church, and navigators all understood a round Earth, and medieval texts routinely describe it as a sphere.

So where did the flat-Earth-in-the-Middle-Ages story come from? Largely the 19th century, when writers, including a popular fictionalized biography of Columbus by Washington Irving, invented or exaggerated the idea to paint the medieval era as ignorant and to dramatize the supposed conflict between science and religion. It stuck because it made a satisfying story of progress. The real Columbus debate was not about shape but about size: educated critics correctly argued the Earth was too big for his planned voyage to Asia to be survivable, and they were right, he only lucked into an unknown continent in the way. Actual flat-Earth belief is overwhelmingly a modern fringe phenomenon, not a medieval consensus.