At the same time that Europe was closing itself off in monasteries, on the eastern side, the Arabs appeared on the historical scene and took over the philosophical heritage of the main cultural centers of the time, under the dominion, until then, of Byzantium or Persia: Alexandria, Antioch, Harran, Edessa and Gundishapur among the main ones.

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            The rapid expansion of Islam followed the union of the Arab peoples in the peninsula with several important victories: Damascus in 635 AD, Jerusalem and Antioch in 638 AD, Mesopotamia in 640 AD and Egypt from 639 to 643 AD. At the other extreme, the Arabs conquered Persia from 637 to 650 AD and, in Europe, in 711 AD, they had already reached southern Spain and were stopped in 732 AD when Charles Martel managed to stop them in France, but they still took Crete in 823 AD and Sicily in 827 AD.

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                 The Arab conquests in the regions dominated by Byzantium surprisingly had the help of the local populations themselves, mainly due to the dissatisfaction of the heretical groups who opposed the oppression exercised by Constantinople over these regions.

 

            The Byzantine Empire became much smaller, but perhaps more homogeneous, as it had rid of the Monophysites and other dissident groups who had been the cause of constant threats to the Empire's disintegration. On the other hand, the various centers of study, culture, philosophy and religion, that had been under Byzantium and the Greek language as the official language, were gradually replaced by the Arabic language.