Every child is taught when Columbus sailed across the Atlantic, the Europeans thought he was crazy because he'd just fall off the side the world. They thought Earth was flat with edges, and it wasn't until he collided with the New World that they realized there's more out there.

I thought that too until as a child I read about Eratosthenes, a Greek mathematician. He had heard at noon on the summer solstice in Syene there were no shadows cast in the well. However there were in Alexandria, where he lived. From that he posited the earth was spherical. From calculating the angles of the shadows in Alexandria and Syene and the distance between them, he was able to figure out surprisingly accurately the circumference of the earth.

So what happened in between? Well, the excuse is after the fall of the Roman Empire, scientific knowledge disappeared in Europe and only started up again during the time of the Renaissance. All right, but as I started studying the Middle Ages this didn't work either. Aristotle, the one ancient philosopher everyone read, said the world was a sphere, and other prominent medieval writers like the Venerable Bede agreed with him. But there was also the belief the world to be a disc, and the sky is a dome called the firmament above it.

Which one is it? Probably a little of both, depending on the time period and the location. I said before Aristotle and some medieval writers said the world was spherical, but that didn't mean everyone read their works. In a time period where many monasteries didn't even have a complete Bible, it's believable that many didn't have access to this knowledge. But in 1492 did people think Columbus would fall off the edge? Nope, they did not. At that point most upper-class people were educated to some extent and knew we lived on a ball, not a disc. What they didn't know about was the Americas, so they just thought Columbus would run out of food in the middle of the ocean before he hit eastern Asia.

What is interesting about this all is Columbus wasn't the first European to discover America. It was the Vikings. By jumping from Greenland, they were able to create some temporary settlements c.1000, but the journey wasn't worth it so they abandoned the project. The New World remained in Icelandic sagas for generations, a hidden gem no one knew about.