Eratosthenes was one of the first to find out that the Earth was round. The way he did it was that the sun would shine to the bottom of a well 2 times a year. So he had someone go to a different well on that day and count his steps. When he got there the sun only reached the side of the well. This showed that the earth was round because if the Earth was flat the sun would shine to the bottom. He then calculated it and found the circumference of the Earth.