GLOBAL CONNECTIONS: the Near/Middle East
622: The Hijra: The Prophet Muhammad moves from Mecca to Medina.

In the Islamic faith, Muhammad is considered the last in a long line of prophets of Allah (God). The Quran, Islam's holy book, is said to have been revealed to Muhammad by the angel Gabriel. The Hijra marks the beginning of the growth of Islam into a world faith. The Muslim calendar counts dates from the Hijra, which is why Muslim dates have the suffix A.H. (After Hijra).

PBS Muhammad
http://www.pbs.org/empires/islam/profilesmuhammed.html

A concise history of Muhammad's life