Responding to Matt J Rossano's latest silliness on Huffington Post, reader Keith Roragen notes that Isidore of Seville (born ca. 560, died 636) described the Earth as a disc, and adds: "Isadore's flat Earth model persisted, at least, into the late 15th century." I have no idea where he's getting the part about Isidore's description of the Earth persisting into the 15th century. At least. I'm quite skeptical about that.
Isidore (AD 560 – 636) wasn't the only medieval Christian who wrote on the subject of the shape of the Earth. Boethius (c. 480 – 524) (possibly not actually a Christian) described it as a sphere. So did the venerable Bede (c.672 – 735) in a treatise on time which circulated widely among the Western monasteries.
And it's not universally agreed that Isidore was talking about a disc and not a sphere. It's also controversial whether Augustine was referring to a sphere or to a disc in his writings.
Pliny the Elder (AD 23-79) says that everyone agreed that the Earth was a sphere, but that it was not entirely clear whether it was a perfect sphere, or something more like the shape of a pine cone.
A few of the pre-Christian Graeco-Romans argued that the Earth was flat, perhaps most prominent among them Lucretius (early 1st century BC), beloved among atheists for remarks like "Fear is the mother of all the gods." Christian writers who argued that the Earth is flat include Lactantius (245–325), St. Athanasius (c.293–373), Diodorus of Tarsus (d. 394), Severian, Bishop of Gabala (d. 408), St.John Chrysostom (344–408) and Cosmas Indicopleustes (6th century). So perhaps the general statement could be made that Christianity set science back several centuries on this topic.
The Christian Basil of Caesarea (AD 329–379) was of the opinion that the question of the shape of the Earth was not theologically important.
It must be added, of course, that with all of the writers mentioned above we are talking about educated people, leading intellectual lights of their times, and that when it comes to the masses, especially the overwhelmingly illiterate masses in the medieval Christian West, it is very hard to tell what they believed.