You will notice that Christianity had extended far eastwards, almost to China.

Most of those eastern Christians were Nestorians and one of their important centres was Edessa, whose school of learning became so celebrated.

Here in the fifth century was built one of the most celebrated hospitals of antiquity.
Now look at another map showing the same countries about a century later.

No such phenomenal change ever was made within so short space of time as that which thus altered the map of Asia and Europe at this period.

Within a century, the Crescent had swept from Arabia through the Eastern Empire, over Egypt, North Africa and over Spain in the West, and the fate of Western Europe hung in the balance before the gates of Tours in 732.