In the late 740s, Basra fell to as-Saffah of the Abbasid Caliphate. During the time of the Abbasids, Basra became an intellectual center and home to the elite Basra School of Grammar, the rival and sister school of the Kufa School of Grammar. Several outstanding intellectuals of the age were Basrans; Arab polymath Ibn al-Haytham, the Arab literary giant al-Jahiz, and the Sufi mystic Rabia Basri. The Zanj Rebellion by the agricultural slaves of the lowlands affected the area. In 871, the Zanj sacked Basra. In 923, the Qarmatians, an extremist Muslim sect, invaded and devastated Basra.