The period covered by this book (AD 381–451) is the first in which the church can be said to have exercised a dominant role in political history. For some it is the period in which the church lost its innocence. Yet without the innovations of Constantine and his successors, it is hard for us to imagine what Christianity might have been. Without this time of consolidation and increasing conformity, Europe would not have existed as we now know it—nor, for that matter, would Islam.