Within twenty years of the flight of the Prophet Muhammad from Mecca to Medina, and only ten years after his death, the recently persecuted adherents of the new Faith embarked on a series of conquests which distinguish the spread of Islam as one of the most important, if not the most important, historical period of the last two thousand years. The conquest of Egypt by the Khalifa Omar was hardly complete in a.d. 641, when the Arabs turned westward along the southern shore of the Mediterranean and became involved in a series of adventures which were destined to menace Europe at a most critical time in its history. The people of Arabia had begun to make another bid for world power which the European branches of Western Man eventually achieved, at their expense.