When the Umayyads, the first Islamic dynasty, rose to power shortly after the death of the Prophet Muhammad (d. 632), the polity of which they assumed control had only recently expanded out of Arabia into the Roman eastern Mediterranean, Iraq and Iran. A century later, by the time of their downfall in 750, the last Umayyad caliphs governed the largest empire that the world had seen, stretching from Spain in the West to the Indus valley and Central Asia in the East. By then, their dynasty and the ruling circles around it had articulated with increasing clarity the public face of the new...