Nizārī Ismāʿīliyyah, commonly called Assassins, religio-political movement that arose between the 11th and the 13th century among the Ismāʿīliyyah, a branch of Shīʿite Islam. Dynastic strife among the Fāṭimids, who were the heads of the Shīʿite Ismāʿīlī movement, resulted in the establishment of a rival caliphate in Egypt in opposition to that of the ʿAbbāsids in Baghdad. After the death of the Fāṭimid caliph al-Mustanṣir (1094), Ḥasan-e Ṣabbāḥ and other Ismāʿīliyyah in Iran refused to recognize the new Fāṭimid caliph in Cairo and transferred their allegiance to his deposed elder brother, Nizār, and the latter’s descendants. There thus grew up