"The expansion of Islam was thus unable to absorb the whole of the Mediterranean. It encircled the Mediterranean on the East, the South, and the West, but it was unable to obtain a hold upon the North. The ancient Roman sea had become the frontier between Islam and Christianity. All the old Mediterranean provinces conquered by the Musulmans gravitated henceforth toward Baghdad. At the same time the Orient was cut off from the Occident. The bond which the Germanic invasion had left intact was severed. Byzantium was henceforth merely the centre of a Greek Empire which could no longer pursue Justinian's policy. It was reduced to defending its last possessions. Its farthest Western outposts were Naples, Venice, Gaeta and Amalfi. The fleet still enabled it to remain in touch with them, and thus prevented the Eastern Mediterranean from becoming a Musulman lake. But the Western Mediterranean was precisely that. Once the great means of communication, it was now an insuperable barrier. Islam had shattered the Mediterranean unity which the Germanic invasions had left intact. This was the most essential event of European history which had occurred since the Punic Wars. It was the end of the classic tradition. It was the beginning of the Middle Ages, and it happened at the very moment when Europe was on the way to becoming Byzantinized."