My speciality is late meieval Scotland. It's a time and place that has poor records compared to its contemporaries (e.g England and France). That said, there's almost nothing of the voice of the commoner in the records. It's the voice of an ecclesiastical elite talking almost exclusively about itself or the lay elite, with an elite audience in mind. I read nothing about what anyone believed regarding the flatness or roundness of the world in the chronicles of Bower or Wyntoun (not that i was looking for it). But the point I want to make is that even if Bower had said, "The peasants and poor city folk believe the world is flat, but they are wrong," you'd have to take it with a grain of salt, because it's not a commoner's voice. It's an elite voice, who certainly had an axe to grind.

This is one of those questions that is equal parts tantalizing and unknowable - at least in the place and time in which I specialized.

One of the staff in my department who specialized in Early medieval Scotland - a time and place with even fewer records than late medieval Scotland - said, and I paraphrase, "You can't ask a question and then go look for the answer in the sources. You'll be frustrated because often you won't find your answer. The primary sources ARE the answers... We have to figure out which questions they go with."

Perhaps someone else, with another specialty can shed some more light.

This question comes up from time to time and I wrote about it awhile back. The short answer is that we have books of collected sermons in the vernacular (that is, not Latin) that mention a spherical earth as a metaphor, from which we can infer that the audience for the sermons (the laity) would be familiar with it as a concept. These date to around the 12th century. Of course the idea of the spherical earth was accepted among the Greek philosophers by the fourth or third century BC.