> I, like you, assumed it was only known to a small group of scholars like Eratosthenes. But digging around a bit, it seems like any literate person in the Mediterranean basin and Middle East during the time of the early Roman Empire could've been exposed to the idea of a spherical earth, via Aristotle or the Pythagoreans.

Don't forget that the literacy rate for pre-modern societies was 10% and probably much lower on average. There were some extreme exceptions, I think the Hebrews had much higher rates, but as a whole, the world's population couldn't even write their own name.