On Fri, Jan 26, 2018, at 11:44, Patrice Scattolin wrote:
Eratosthene measured the earth diameter somewhere around 200BC https://en.wikipedia.org/wiki/Eratosthenes#Measurement_of_the_Earth's_circumference
A better question to ask is when circular earth became dominant belief. That, I am not aware of good documentation. That said, Columbus knew the earth to be round so it wasn't super obscure knowledge.
My understanding is: Everyone educated knew the world was round. Columbus believed, wrongly, that it was smaller than the actual size and therefore that it was practical to reach East Asia by sailing across what he believed to be an open ocean. The consensus view on Earth's diameter was more accurate, which is why he had trouble getting funding.