The special authority that the bishop of Rome assumed was that of supreme pontiff (<em>pontifex maximus</em>) or pope. The pope is the leader of the Catholic Church, and also the head of state of Vatican City. The current pope is Pope Francis. The pope, as bishop of Rome, is considered the succesor of Saint Peter.
Military conquests by the Arab Empire and traders of Islamic faith were the primary means for spreading Islam to Africa, Europe, and Asia. I think its this one
