The fantasy of Washington Irving of the untutored sailor instructing the wise scholars of Europe that the Earth was round had, as its basis in fact, that there was indeed an argument.
But it was not over if the Earth was round, it was about how FAR around it was. Columbus incorrectly assumed the figure of Erotosthenes was an overestimation. The wise scholars correctly pointed out to Columbus that if Erotosthenes was correct (and he was), Columbus would never make it to India.... and he wouldn't have.
So any lettered person who was from the time of Christ onward would know, not only that the Earth was round, they would know how far around it was.
But it is WAY more fun to present those evil, ignorant, superstitious, hag-ridden-by-the-Vatican(how do you type a sneer?) priests of thinking the world was flat and Columbus gonna sail of the edge.
I've always been impressed with Eratosthenes's arithmetic, moiself.