Al-Mustaʿlī biʾllāh (15/16 September 1074 – 1101) was the ninth Fatimid caliph and the nineteenth imam of Musta'li Ismailism. He became caliph through the machinations of his brother-in-law al-Afdal Shahanshah. In response, his oldest brother, Nizar, revolted in Alexandria; his defeat and execution split the Isma'ili movement. Al-Musta'li remained subordinate to al-Afdal, who was the de facto ruler of the Fatimid Caliphate. The Caliphate's territory in Egypt experienced good government and prosperity, but the Fatimids suffered setbacks in Syria, where they faced the advance of the Seljuk Turks. Al-Afdal recovered the port city of Tyre and recaptured Jerusalem in the turmoil caused by the arrival of the First Crusade. Despite Fatimid attempts to make common cause with the Crusaders against the Seljuks, the Crusaders advanced south and captured Jerusalem in July 1099 and defeated the Fatimid army at the Battle of Ascalon. Al-Musta'li died in 1101 and was succeeded by his son al-Amir. (Full article...)