The worship of Isis and Osiris was prominent in ancient Egyptian religion long before the entrance of Greek influence. Osiris was regarded as the ruler over the dead, and as such was naturally very important in a religion in which supreme attention was given to a future life. But with the establishment of the Ptolemaic kingdom at about 300 B. C., there was an important modification of the worship. A new god, Serapis, was introduced, and was closely identified with Osiris. The origin of the name Serapis has been the subject of much discussion and is still obscure. But one motive for the introduction of the new divinity (or of the new name for an old divinity) is perfectly plain. Ptolemy I desired to unify the Egyptian and the Greek elements in his kingdom by providing a cult which would be acceptable to both and at the same time intensely loyal to the crown. The result was the Greco-Egyptian cult of Serapis (Osiris) and Isis. Here is to be found, then, the remarkable phenomenon of a religion deliberately established for political reasons, which, despite its artificial origin, became enormously successful. Of course, the success was obtained only by a skillful use of existing beliefs, which had been hallowed in Egyptian usage from time immemorial, and by a skillful clothing of those beliefs in forms acceptable to the Greek element in the population. The religion of Isis and Serapis was, as Cumont observes, entirely devoid of any established system of theology or any very lofty ethics. It was effective rather on account of its gorgeous ritual, which was handed down from generation to generation with meticulous accuracy, and on account of the assurance which it gave of a blessed immortality, the worshipers being conceived of as sharing in the resuscitation which Osiris had obtained. The worship was at first repulsive to Roman ideals of gravity, but effected an official entrance into the city in the reign of Caligula (37-41 A. D.). In the second and third centuries it was extended over the whole Empire. In alliance with the religion of Mithras it became finally perhaps the most serious rival of Christianity. The cult was partly public and partly private. Prominent in the public worship were the solemn opening of the temple of Isis in the morning and the solemn closing in the afternoon. Elaborate care was taken of the images of the gods--the gods being regarded as dependent upon human ministrations. Besides the rites that were conducted daily, there were special festivals like the spring festival of the "ship of Isis" which is brilliantly described by Apuleius.