Almost 1,400 years ago, the established world order was overturned by the emergence of a dynamic new power in the Near East. From the mid-630s, fearsome bands of Arab tribesmen began to pour out of their homelands in the Arabian Peninsula. Within a few decades these highly mobile, mounted warriors achieved startling successes – overrunning Palestine, Syria, Iraq, Iran and Egypt with mercurial speed – and, by the middle of the next century, their descendants could claim dominion over a vast swathe of territory, stretching from the Indus River and the borders of China in the east, across north Africa to Spain and southern France in the west.

An explanation for this explosive, seemingly unheralded phenomenon has long been sought. How was it that the Arabs – previously a known, but relatively insignificant, force on the world stage – suddenly became invincible conquerors? What lent them the unity of purpose and martial vigour to topple the ancient might