You know, Dante and Chaucer knew the world was round. I think a lot of the stuff about people thinking it was flat is a part of the "Aren't we simply marvellous?" strand of self-congratulatory thought that starts (very well) with Pico della Mirandola but doesn't hit its stride until the 19th century. I WOULD Like to know who in the west knew the world was round before we got access to the Muslim Libraries, but I bet they never forgot in Easter "Christendom".
You are right. Ptolemy taught of the rotating spheres. So, the concept of flat earth somehow coexisted with the roundness of the world as a whole. Indeed, as one observes the sky with the naked eye, he sees the visible universe round, but the earth flat.