 From the second century AD, there was a movement of tribes from Al Bahreyn towards the lower Gulf, together with a migration among the Azdite Qahtani (or Yamani) and Quda'ah tribal groups from south-west Arabia towards central Oman.The spread of Islam to the North Eastern tip of the Arabian Peninsula is thought to have followed directly from a letter sent by the Islamic Prophet, Muhammad, to the rulers of Oman in 630 AD, nine years after the hijrah.This led to a group of rulers travelling to Medina, converting to Islam and subsequently driving a successful uprising against the unpopular Sasanids, who dominated the Northern coasts at the time.