The event where Muhammad fled Mecca with a small group of followers to go to Medina (Yathrib) in the year 622 A.D., under mounting hostility towards Muhammad. Muslim calendars dates from this date (A.H.), which was established in `Umar's reign. Medina is about 200 miles north of Mecca, and they had invited Muhammad to go there. Muhammad arrived there on 20th Sep 622 A.D, and the name of the city was changed to Medinatu'l-Nabi (city of the Prophet).