Azazeel by Youssef Ziedan. It's a tale set in 5th-century Egypt and the Levant, following a coptic monk’s journey amidst the theological controversies of the early Christian curch. Apart from the protagonist (and his devilish visitor) I think all the characters are historically real as well as for the events. It's a very interesting period during which Christians, Jews and Atheists coexisted, although perturbently.