Here’s an article from Jeffrey Burton Russell.

Excerpt:

It must first be reiterated that with extraordinary few exceptions no educated person in the history of Western Civilization from the third century B.C. onward believed that the earth was flat.

A round earth appears at least as early as the sixth century BC with Pythagoras, who was followed by Aristotle, Euclid, and Aristarchus, among others in observing that the earth was a sphere. Although there were a few dissenters–Leukippos and Demokritos for example–by the time of Eratosthenes (3 c. BC), followed by Crates(2 c. BC), Strabo (3 c. BC), and Ptolemy (first c. AD), the sphericity of the earth was accepted by all educated Greeks and Romans.

Nor did this situation change with the advent of Christianity. A few–at least two and at most five–early Christian fathers denied the sphericity of earth by mistakenly taking passages such as Ps. 104:2-3 as geographical rather than metaphorical statements. On the other side tens of thousands of Christian theologians, poets, artists, and scientists took the spherical view throughout the early, medieval, and modern church. The point is that no educated person believed otherwise.

Historians of science have been proving this point for at least 70 years (most recently Edward Grant, David Lindberg, Daniel Woodward, and Robert S. Westman), without making notable headway against the error. Schoolchildren in the US, Europe, and Japan are for the most part being taught the same old nonsense. How and why did this nonsense emerge?

In my research, I looked to see how old the idea was that medieval Christians believed the earth was flat. I obviously did not find it among medieval Christians. Nor among anti-Catholic Protestant reformers. Nor in Copernicus or Galileo or their followers, who had to demonstrate the superiority of a heliocentric system, but not of a spherical earth. I was sure I would find it among the eighteenth-century philosophes, among all their vitriolic sneers at Christianity, but not a word. I am still amazed at where it first appears.

No one before the 1830s believed that medieval people thought that the earth was flat.

The idea was established, almost contemporaneously, by a Frenchman and an American, between whom I have not been able to establish a connection, though they were both in Paris at the same time. One was Antoine-Jean Letronne (1787-1848), an academic of strong antireligious prejudices who had studied both geography and patristics and who cleverly drew upon both to misrepresent the church fathers and their medieval successors as believing in a flat earth, in his On the Cosmographical Ideas of the Church Fathers (1834). The American was no other than our beloved storyteller Washington Irving (1783-1859), who loved to write historical fiction under the guise of history. His misrepresentations of the history of early New York City and of the life of Washington were topped by his history of Christopher Columbus (1828). It was he who invented the indelible picture of the young Columbus, a “simple mariner,” appearing before a dark crowd of benighted inquisitors and hooded theologians at a council of Salamanca, all of whom believed, according to Irving, that the earth was flat like a plate. Well, yes, there was a meeting at Salamanca in 1491, but Irving’s version of it, to quote a distinguished modern historian of Columbus, was “pure moonshine. Washington Irving, scenting his opportunity for a picturesque and moving scene,” created a fictitious account of this “nonexistent university council” and “let his imagination go completely…the whole story is misleading and mischievous nonsense.”

But now, why did the false accounts of Letronne and Irving become melded and then, as early as the 1860s, begin to be served up in schools and in schoolbooks as the solemn truth?

The answer is that the falsehood about the spherical earth became a colorful and unforgettable part of a larger falsehood: the falsehood of the eternal war between science (good) and religion (bad) throughout Western history. This vast web of falsehood was invented and propagated by the influential historian John Draper (1811-1882) and many prestigious followers, such as Andrew Dickson White (1832-1918), the president of Cornell University, who made sure that the false account was perpetrated in texts, encyclopedias, and even allegedly serious scholarship, down to the present day. A lively current version of the lie can be found in Daniel Boorstin’s The Discoverers, found in any bookshop or library.

The reason for promoting both the specific lie about the sphericity of the earth and the general lie that religion and science are in natural and eternal conflict in Western society, is to defend Darwinism. The answer is really only slightly more complicated than that bald statement. The flat-earth lie was ammunition against the creationists. The argument was simple and powerful, if not elegant: “Look how stupid these Christians are. They are always getting in the way of science and progress. These people who deny evolution today are exactly the same sort of people as those idiots who for at least a thousand years denied that the earth was round. How stupid can you get?”

But that is not the truth.

What’s scary about this is that I have actually debated with atheists who have cited Bugs Bunny cartoons showing the Columbus flat-Earth scene as an authority for this persistent myth. I think it’s safer to stick with a historian. Dr. Russell has written a book about “The Myth of the Flat Earth” and he has also been published by Oxford University Press and Cornell University Press and Princeton University Press – unlike the Bugs Bunny cartoon artists.