Ismāʿīl al-ʿUkbarī, who was active during the reign of the Abbasid caliph al-Muʿtaṣim (r. 833–842),  founded one of the many Jewish sects that came into being in Babylonia at the beginning of the gaonic period. The sect was no longer in existence by the first half of the tenth century. What little is known about it is derived from Karaite and, to a lesser extent, Muslim sources.   Al-ʿUkbarī’s movement was apparently messianic in nature, as can be inferred from the instructions he gave his followers to inscribe the phrase “the chariots of Israel and the horsemen th…