Who said that the earth is round?

Leave it to the clever Greek investigator Eratosthenes to bring it all together with a calculation (and a remarkably accurate one!) about the diameter of the earth, and also the inclination of its axis of rotation to its orbital plane about the sun. Amazing! And later in Medieval Europe, the earth was thought to be flat. What happened? You'll want to check facts and read more on the geodesy ("roundness") of the earth, and a link is provided to the Wikipedia article on exactly that subject.