This book is a history of the rituals by which the first Muslim monarchs were formally acknowledged. Like the Christian Roman emperor and the Iranian King of Kings, the caliph of the first Muslim empire was acclaimed by his followers and received oaths of allegiance from them. He appeared before them enthroned in both religious and royal settings, bearing the insignia of his office. That the caliph was a ‘monarch’, and in some senses a ‘king’, perhaps does not need to be restated. However, the emphasis in much of Islamic political thought on the notion of ‘kingship’ (mulk) as mere earthly, or temporal power, in contrast to the legitimate authority of the ‘caliphate’ (khilāfa), which is derived from God, can obscure the important continuities between caliphal authority and that of ancient Near Eastern monarchy. Because of this distinction in the Islamic tradition, ‘monarchy’ is probably a better description of the caliphate than ‘kingship’; it encompasses the shared cultural heritage with ancient Near Eastern rulership, while acknowledging the distinctive semantic and conceptual transformations of that heritage that took place in Islam.

The monarchs of Rome, Iran and Islam each represented temporal and sacral authority in an imperial context – they were both ‘king’ and ‘priest’ of a preeminent, divinely sanctioned world power. In Islam, a division of roles between the caliph and his Muslim subjects eventually led to ‘classical’ Sunni orthodoxy (that is, the four main schools of medieval Sunni Islam), in which the right to interpret God's law (sharica) came to reside not exclusively in the person of the caliph, but rather in God's community as a whole.