I agree with Columbus. The world has definitely gone pear shaped.

Fry is almost certainly correct that modern ideas of the middle ages are overstating things. Certainly scholars of the time had sources available describing the earth as a sphere.

I was told the confusion stemmed from Isidore of Seville who wrote a book called the Etymologies, in Latin, to summarise the Greek books from classical antiquity. This was becoming important at a time when Greek was studied much less, and the originals were therefore inaccessible to most scholars. Anyway, in one passage of his Etymologies he described the shape of the earth as being round, like a wheel.

This probably didn't cause nearly as much confusion as people think.