The Muslims of Syria, who were the first to receive the assault of the Crusaders, thought the invaders were Rum, the Byzantines. Accordingly, they regarded the invasion as still another Byzantine incursion into Islamic territory, and, in fact, one inspired by previous Muslim victories in Byzantine domains. It was only when the Muslims realized that the invaders did not originate in Byzantium that they began referring to them as Franks, although never as Crusaders, a term for which there was no Arabic equivalent until modern times. Even a century later, the Arab historian Ibn al-Athīr (1160–1233) characterized that first invasion as a part of the general expansion of the Frankish empire that had begun with their conquests in Muslim Spain, Sicily, and North Africa a decade before the campaign in Syria. Nevertheless, the establishment of Frankish kingdoms in Islamic territory, the periodic reinforcement of troops from...