The Rashidun (‘Rightly Guided’) were five close companions of the prophet Muhammad who were, successively, caliphs during the expansion of the Islamic Empire (632–61). The empire dissolved into civil war with the assassination of Caliph Uthman (656–61 (the ‘first Fitna’) and again with the death of the first Umayyad caliph, Muawiya (680–92). These conflicts arose from the frustrated claims to the caliphate of Husayn ibn Ali, Muhammad’s grandson. Husayn was killed at Kerbela (680) and his cause would become the foundation of Shi’ism. Apart from causing occasional moratoria, these internal dissensions did not impede Islamic conquest. The Rashidun were blessed with superb generals with battle-hardened, ethnically cohesive, armies fired by religious fervour. They repeatedly defeated the mercenary armies of their imperial rivals, the Sassanids and Byzantines, ruling from the River Indus to Sicily by Uthman’s death. Most impressively, these desert warriors mastered marine warfare, routing the Byzantine navy (654).