Before 622 CE the oasis settlement of Yathrib was divided among Arab and Jewish tribes with no single ruling authority. Muhammad's migration there that year, the Hijra, is the event from which the Islamic calendar counts its years, and it transformed the town into what came to be called Al Madinah al Munawwarah, the Enlightened City, or simply Medina, the City.
Shortly after his arrival Muhammad drew up what is generally called the Constitution of Medina, an agreement setting out mutual obligations among the Muslim emigrants from Mecca, the Medinan converts known as the Ansar, and the city's Jewish tribes, establishing the new community as a single political body under his arbitration. Medina remained Muhammad's base for the rest of his life, the city from which the early Muslim community organized itself, sent out its first military expeditions, and received the bulk of the Quranic revelations later classified as Medinan surahs, distinguished by scholars from the earlier Meccan ones by their concern with law and communal governance rather than doctrine alone. Muhammad died in Medina in 632 CE and was buried in the chamber of Aisha's house adjoining the mosque, a site now enclosed within the Prophet's Mosque itself. The city then served as the capital of the Muslim community under the first four caliphs, until Ali's caliphate moved the center of gravity to Kufa and the Umayyads later moved it to Damascus, leaving Medina a city of memory and pilgrimage rather than government.