This is interesting: https://en.wikipedia.org/wiki/Myth_of_the_flat_Earth. But what about non-scholars; what did they think?
Common people in middle age Europe, at least, knew the world was round. I wrote about this before: https://www.reddit.com/r/AskHistorians/comments/3g5hpj/educated_people_in_the_middle_ages_knew_that_the/
Let me know if you have follow-up questions.