of places such as Iraq (then called Mesopotamia), Egypt, and Syria as Muslim, we forget that they were once the heartland of the Christian world. In the fourth century one could still speak of a single Christian world. But in the fifth century, when Germanic and similar tribes invaded and conquered the western part of the Roman Empire, centered on Rome, the slow division began between Western, Latin-speaking Christianity, which we now call Catholicism, and that of the East Roman Empire, which lasted,