As Koelle has pointed out, there is no reason to suppose that his principles in any way changed, but under the altered conditions and environment the utterly non-ethical theory of revelation held by the prophet became more apparent. This is perhaps most clearly brought out by his utterly unscrupulous dealing with the Jews, and also by the story of Zaid and Zainab, in all which affairs Mohammed professed himself to be acting under Divine direction, nor is it at all obvious that he did not actually believe it. Finally, before his death, he succeeded in establishing his religion and political system throughout the whole of Arabia. Of course it was impossible for a movement like this to take place without rival prophets appearing in other parts of the country. Two of these appeared during Mohammed’s lifetime, and he thought it best to guard against future schisms of a similar kind by declaring himself the last of the prophets. Exactly what he meant by this is not very clear: if the almost universal voice of Islam is to be accepted, he did not mean that he was the last divinely appointed teacher, for all Mussulmans look forward to the coming of a Mehdi or Mahdi, who, together with Jesus, the son of Mary, is to appear in the last days, and spread the doctrines of Islam throughout the world. Orthodox Mussulmans, however, always look upon Mohammed as the last great _sāhibi kitāb_, or book-bearer. The ordinary Sunnis, who are the largest and best-known Mussulman sect, assert that, as a matter of fact, since the time of Mohammed, no divinely-appointed teacher has as yet appeared. The Khalīfs were in their eyes simply appointed by the congregation, and the four great writers of the _sunnat_, which is to them the only authoritative commentary upon the doctrines of Islam, were only learned and saintly men. Now, they hold, these doctrines can only be learnt from this book, and from the _Qurān_ itself; for the _mujtahid_ or high mulla, capable of giving authoritative decisions on moot points, no longer exists. The Shiahs have very different tenets. Mohammed according to their teaching was the first of a hierarchic dynasty of thirteen, consisting of himself and the twelve great Imāms, of whom the first was Ali, the son-in-law of the prophet, and who were all as certainly divinely appointed as Mohammed himself. Mohammed is only the last great book-bearer, and therefore the founder of the present era. The last of the Imams was the Mehdi, who according to the Sunnis has not yet been born, but according to the Shiahs appeared long ago. This man did not die, but disappeared, remaining at first accessible to his followers through the medium of four successive Bābs, or gates of knowledge, who were in touch with him during his concealment. Like the Imams, the Babs came to an end, for the last of them refused to appoint a successor. All this of course is very ancient history.