Hegira

Hegira (from the Arabic hijra, which means breaking off relations, abandoning one's tribe, "flight" or migrating) refers to the departure of the Prophet Muhammad from Mecca in AD 622. His criticism of the polytheism of the Meccan religion had angered the merchants of Mecca, who were reaping large profits from pilgrims. Forced into exile, Muhammad went to Yathrib (later renamed Medina) and became its ruler. The caliph Umar I (d. 664) proclaimed the start of the Muslim era (dated AH, annus hegirae) from the first day (July 16, 622, by the Julian calendar) of the lunar year, in which the hegira occurred. The term is also applied to any Muslim emigration.