THE EXPANSION OF ISLAM IN THE
Nothing could be more suggestive, nothing could better enable us to comprehend the expansion of Islam in the 7th century, than to compare its effect upon the Roman Empire with that of the Germanic invasions. These latter invasions were the climax of a situation which was as old as the Empire, and indeed even older, and which had weighed upon it more or less heavily throughout its history. When the Empire, its frontiers penetrated, abandoned the struggle, the invaders promptly allowed themselves to become absorbed in it, and as far as possible they maintained its civilization, and entered into the community upon which this civilization was based.
On the other hand, before the Mohammedan epoch the Empire had had practically no dealings with the Arabian peninsula.1 It contented itself with building a wall to protect Syria against the nomadic bands of the desert, much as it had built a wall in the north of Britain in order to check the invasions of the Picts; but this Syrian limes, some remains of which may still be seen on crossing the desert, was in no way comparable to that of the Rhine or the Danube.2
The Empire had never regarded this as one of its vulnerable points, nor had it ever massed there any large proportion of its military forces. It was a frontier of inspection, which was crossed by the caravans that brought perfumes and spices. The Persian____________________