840s in the Abbasid Caliphate

thumb|right|300px|Map of the Mihna and events associated with itThe Mihna () was a period of religious persecution instituted by the Abbasid caliph al-Ma'mun in 833 in which Sunni scholars were punished, imprisoned, or even killed unless they conformed to Mu'tazilite doctrine. The policy lasted for eighteen years (833–851) as it continued through the reigns of al-Ma'mun's immediate successors, al-Mu'tasim and al-Wathiq, and four years of al-Mutawakkil who reversed it in 851.

group of christian Martyrs

844 battle of the Arab-Byzantine Wars

Earthquake affecting Syria and Lebanon