i think there was a greek(?) guy who made a map of all known locations on earth in the 3rd century AD, and in the preamble he stated that the earth was a sphere, and he almost got the diameter correctly, he only estimated it to be 25% less than it actually is (same order of magnitude though).

1200 years later columbus read that stuff and thought "huh, okay, based on this diameter i can sail to india no problem". even though it was known at the time that the diameter would have to be higher, columbus kinda willfully ignored it (wishful thinking). and got lucky.