Then suddenly a change came over the character of the Arabs. No longer courting seclusion, they came forth before the world, and proceeded in good earnest to conquer it. The change had been caused by one man. Mohammed the Arabian Prophet began to preach the religion of _Islam_ in the beginning of the seventh century, and his doctrine, falling upon a people prone to quick impulses and susceptible of strong impressions, worked a revolution. What he taught was simple enough. He took the old faith of the Hebrews, which had its disciples in Arabia, and, making such additions and alterations as he thought needful, he preached the worship of One God as a new revelation to a nation of idolaters. It is difficult for us in the present time to understand the irresistible impulse which the simple and unemotional creed of Mohammed gave to the whole people of Arabia; but we know that such religious revolutions have been, and that there is always a mysterious and potent fascination in the personal influence of a true prophet. Mohammed was so far true, that he taught honestly and strenuously what he believed to be the only right faith, and there was enough of sublimity in the creed and of enthusiasm in the Prophet and his hearers to produce that wave of overmastering popular feeling which people call fanaticism. The Arabs before the time of Mohammed had been a collection of rival tribes or clans, excelling in the savage virtues of bravery, hospitality, and even chivalry, and devoted to the pursuit of booty. The Prophet turned the Arab tribes, for the nonce, into the Moslem people, filled them with the fervour of martyrs, and added to the greed of plunder the nobler ambition of bringing all mankind to the knowledge of the truth. Before Mohammed died he was master of Arabia, and the united tribes who had embraced the Moslem or Mohammedan faith were already spreading over the neighbouring lands and subduing the astonished nations. Under his successors the Khalifs, the armies of the Mussulmans overran Persia and Egypt and North Africa as far as the Pillars of Hercules; and the Muezzins chanted the Call to Prayer to the Faithful over all the land from the river Oxus in Central Asia to the shores of the Atlantic Ocean.