For as long as there has been urban civilisation in the Fertile Crescent, there have been bandits eager to plunder its riches. In 610 AD, for instance, a raid was launched by a war band of Arabs on Syria. ‘They pillaged and laid waste many lands, committed many massacres of men and burned without compassion or pity.’ Much the same might have been recorded by chroniclers writing in the Bronze Age or by journalists today covering the depredations of ISIS. Nevertheless, over the course of history, raiders from the sands beyond Syria or Iraq have rarely managed to establish enduring empires. The reason for this is obvious: the immense preponderance of wealth and manpower that settled communities always tend to enjoy over nomads. Violent tides may race in from the desert, but invariably they also ebb. 

In the 7th century AD, though, something exceptional happened. Three decades on from the raid of 610, Arab war bands succeeded in conquering the whole of Syria. A century on and they had come to rule an empire that stretched from the Atlantic to central Asia. So astonishing was this