1) Educated people believed the world was round long before 1492. As far back as the ancient Greeks scholars tried to estimate the circumference of the Earth.
2) Even the lowliest serf knew about Jerusalem and Israel, even if they didn't know where it was in relation to their village.
4) If the OP is using Merlin as the magician, tradition has it he lived backwards and thus knew the future, because he'd been there.
OP, this entry at Wikipedia should give you a good overview of how the ancients viewed the world and you can extrapolate what you need from that.
quibbles
2) Even the lowliest serf knew about Jerusalem and Israel, even if they didn't know where it was in relation to their village.
4) If the OP is using Merlin as the magician, tradition has it he lived backwards and thus knew the future, because he'd been there.
OP, this entry at Wikipedia should give you a good overview of how the ancients viewed the world and you can extrapolate what you need from that.