The movement reached its political height during the Mihna, the period of religious persecution instituted by the 'Abbasid Caliph al-Ma'mun in AD 833 in which religious scholars (such as Sunnis and Shias) were punished, imprisoned, or even killed unless they conformed to Muʿtazila doctrine. The policy lasted for 18 years (833–851 CE) as it continued through the reigns of al-Ma'mun's immediate successors, al-Mu'tasim and al-Wathiq, and the first four years of the reign of al-Mutawakkil, who reversed the policy in 851. (PDF)
