When Columbus set sail in 1492, he proved - for the first time - that Earth was round. Europeans laughed at Columbus, certain he would fall off the edge of the flat Earth. If you've heard that story, you aren't alone. There's just one problem: It's completely false. Dating back to the 6th century, educated Greeks, Romans, and medieval Europeans knew Earth was a sphere. Medieval Christian writers explained Earth was like a ball, and scientists even calculated Earth's circumference with remarkable accuracy.
Long before Columbus, Europeans made globes, which would be pretty strange if they thought Earth was flat. And educated people weren't the only ones who knew Earth was round. Even illiterate sailors didn't believe Earth was flat for a simple reason.
In fact, bizarre flat-Earther theories are much newer than the 15th century. Most of them come from a 19th-century hoax invented by the same guy who came up with the Headless Horseman. But proof that medieval people knew Earth was round probably won't sway flat-Earthers who've attempted to justify a patently silly theory.
Proof that Earth is round dates back millennia. In the year 240 BCE, a Greek scientist estimated the size of Earth to within about 4,000 miles, thanks to simple math. Eratosthenes of Cyrene set up his experiment carefully. On the longest day of the year, June 19, Eratosthenes measured the angle of the shadow on a sundial in the city of Alexandria, Egypt, calculating it was 1/50th of a circle.
He then estimated the circumference of Earth using the distance between Alexandria and Syene, Egypt, where the sun was at its zenith and cast no shadow. Based on his shadow measurement, Eratosthenes estimated Earth was about 28,968 miles in circumference, impressively close to the actual distance of 24,902 miles.
Educated medieval Europeans knew Earth was round. But what about uneducated people? Illiterate sailors and merchants also knew Earth's shape. For sailors, it was simply common sense: When a ship sailed away, its hull vanished before its mast. City designers knew the same thing, as they built tall lookout towers near their ports so they could sight incoming ships sooner. After all, you can see more of a ship from a high tower than from sea level.
In fact, the first people to know Earth was curved might have been ancient sailors, who saw proof of the curve before ancient Greek philosophers began theorizing.
Washington Irving, famous for The Legend of Sleepy Hollow, single-handedly invented the myth that Columbus proved Earth wasn't flat. In 1828, Irving published The Life and Voyages of Christopher Columbus. In the book, Irving made Columbus sound heroic by portraying him as a Galileo-like figure who insisted in the face of Catholic opposition that Earth was round.
In his story, Irving makes a Catholic geographer blurt out, "Is there anyone so foolish, as to believe [in] people who walk with their heels upward, and their head hanging down?"
Every educated geographer in the 15th century knew Earth was round, but Irving's fiction persists nearly two centuries later.
In the 19th century, Antoine-Jean Letronne promoted the rumor that medieval Europeans thought Earth was flat. A French academic, Letronne was a committed anticlericalist who targeted the Catholic Church in his writings. Letronne used the flat-Earth theory to smear the church for suppressing scientific knowledge.
In "On the Cosmological Opinions of the Church Fathers," an article published in 1834, Letronne declared medieval Christians believed Earth was flat due to the church's suppression of science. Letronne's ideologically motivated tactic helped cement the idea of a backward "Dark Ages."