August 15 [marked] the anniversary of Constantinople’s victory over Muslim invaders in what historians commonly call the “Second Siege of Byzantium,” 717–18. Prior to this massive onslaught, the Muslims had been hacking away at the domains of the Byzantine empire for nearly a century. The Muslims’ ultimate goal was the conquest of Constantinople — for both political and religious reasons.
Politically, Islam had no rival but the “hated Christians” of Byzantium, known by various appellations — including al-Rum (the Romans), al-Nassara (the Nazarenes), and, most notoriously, al-Kilab (the “dogs”). The eastern Sasanian Empire had already been vanquished, and Persia subsumed into the caliphate. Only the “worshippers of the cross” — as they were, and still are, disparagingly known — were left as contenders over the eastern Mediterranean basin.
More important, Constantinople — from a theological perspective — simply had to fall. From the start, Islam and jihad were inextricably linked. The jihad, or “holy war,” which took over Arabia and Persia, followed by Syria, Egypt, and all of North Africa — all formerly Byzantine territory — was considered a religious obligation, or, as later codified in sharia law, a fard kifaya: a communal obligation on the body of believers, to be adhered to and fulfilled no less than the Five Pillars of Islam. As the famous 14th-century Muslim historian Ibn Khaldun put it: “In the Muslim community, the jihad is a religious duty, because of the universalism of the Muslim mission and the obligation to convert everybody to Islam either by persuasion or by force. . . . Islam is under obligation to gain power over other nations.”