Islam began in the small desert town of mecca ,now Saudi Arabia and surrounded by the Sassanian empires and Byzantine ,that islam emerged in the early 7th century through revelation that muslims believe were made to islam's prophet, Muhammed, by the archangel Gibril.
Muhammed began receiving revelations in 610 while he was meditating in a cave on the summit of mount Hira, muslims believe that those revelations are the words of God, conveyed by Gibril, and that they constitute the Koran, islam's holly book .
Muhammad only confided in his wife and friends they he had received the revelations, and it was more than two years later that he started preaching publicly.