During the 1920s Belgian historian Henri Pirenne came to an astonishing conclusion: the ancient classical civilization, which Rome had established throughout Europe and the Mediterranean world, was not destroyed by the Barbarians who invaded the western provinces in the fifth century, it was destroyed by the Arabs, whose conquest of the Middle East and North Africa terminated Roman civilization in those regions and cut off Europe from any further trading and cultural contact with the East. According to Pirenne, it was only in the mid-seventh century that the characteristic features of...