Ancient man wasn’t stupid.
Earth 500 years ago
The myth of the Flat Earth is the modern misconception that the prevailing cosmological view during the Middle Ages saw the Earth as flat, instead of spherical.
This idea seems to have been widespread during the first half of the 20th century, so that the Members of the Historical Association in 1945 stated that:
“The idea that educated men at the time of Columbus believed that the earth was flat, and that this belief was one of the obstacles to be overcome by Columbus before he could get his project sanctioned, remains one of the hardiest errors in teaching.”
During the early Middle Ages, virtually all scholars maintained the spherical viewpoint first expressed by the Ancient Greeks. By the 14th century, belief in a flat earth among the educated was essentially dead.
However, among Medieval artists, depictions of a flat earth remained common. The exterior of the famous triptych The Garden of Earthly Delights by Hieronymus Bosch is a Renaissance example in which a disc-shaped earth is shown floating inside a transparent sphere.
According to Stephen Jay Gould, “there never was a period of ‘flat earth darkness’ among scholars (regardless of how the public at large may have conceptualized our planet both then and now). Greek knowledge of sphericity never faded, and all major medieval scholars accepted the earth’s roundness as an established fact of cosmology.”
Historians of science David Lindberg and Ronald Numbers point out that “there was scarcely a Christian scholar of the Middle Ages who did not acknowledge [Earth’s] sphericity and even know its approximate circumference”.
Historian Jeffrey Burton Russell says the flat earth error flourished most between 1870 and 1920, and had to do with the ideological setting created by struggles over evolution.
Russell claims “with extraordinary [sic] few exceptions no educated person in the history of Western Civilization from the third century B.C. onward believed that the earth was flat,” and credits histories by John William Draper, Andrew Dickson White, and Washington Irving for popularizing the flat-earth myth.
(via Myth of the Flat Earth)