As thus described, the worship of Cybele and Attis was, for the most part at least, public. But there were also mysteries connected with the same two gods. These mysteries apparently were practised in the East before the cult was brought to Rome. But the eastern form of their celebration is quite obscure, and even about the Roman form very little is known. Connected with the mysteries was some sort of sacred meal.[144] Firmicus Maternus has preserved the formula: "I have eaten from the drum; I have drunk from the cymbal; I have become an initiate of Attis."[145] And Clement of Alexandria (about 200 A. D.) also connected a similar formula with the Phrygian mysteries: "I ate from the drum; I drank from the cymbal; I carried the 'kernos'; I stole into the bridal chamber."[146] The significance of this ritual eating and drinking is not clear. Certainly it would be rash to find in it the notion of new birth or sacramental union with the divine nature. Hepding suggests that it meant rather the entrance of the initiate into the circle of the table-companions of the god.

The actual initiation is even more obscure in the Attis mysteries than it is in those of Eleusis; Hepding admits that his reconstruction of the details of the mysteries is based largely on conjecture. Possibly in the formula quoted above from Clement of Alexandria, the words, "I stole into the bridal chamber," indicate that there was some sort of representation of a sacred marriage; but other interpretations of the Greek words are possible. Hepding suggests that the candidate entered into the grotto, descended into a ditch within the grotto, listened to lamentations for the dead god, received a blood-bath, then saw a wonderful light, and heard the joyful words quoted above: "Be of good courage, ye initiates, since the god is saved; for to us shall there be salvation out of troubles," and finally that the candidate arose out of the ditch as a new man ("reborn for eternity") or rather as a being identified with the god.[147]

According to this reconstruction, the initiation represented the death and the new birth of the candidate. But the reconstruction is exceedingly doubtful, and some of the most important features of it are attested in connection with the Attis mysteries if at all only in very late sources. Hepding is particularly careful to admit that there is no direct documentary evidence for connecting the blood-bath with the March festival.

This blood-bath, which is called the taurobolium, requires special attention. The one who received it descended into a pit over which a lattice-work was placed. A bull was slaughtered above the lattice-work, and the blood was allowed to run through into the pit, where the recipient let it saturate his clothing and even enter his nose and mouth and ears. The result was that the recipient was "reborn forever," or else reborn for a period of twenty years, after which the rite had to be repeated. The taurobolium is thought to have signified a death to the old life and a new birth into a higher, divine existence. But it is not perfectly clear that it had that significance in the East and in the early period. According to Hepding, the taurobolium was in the early period a mere sacrifice, and the first man who is said to have received it in the sense just described was the Emperor Heliogabalus (third century after Christ). Other scholars refuse to accept Hepding's distinction between an earlier and a later form of the rite. But the matter is at least obscure, and it would be exceedingly rash to attribute pre-Christian origin to the developed taurobolium as it appears in fourth-century sources. Indeed, there seems to be no mention of any kind of taurobolium whatever before the second century,[148] and Hepding may be correct in suggesting that possibly the fourth-century practice was influenced by the Christian doctrine of the blood of Christ.[149]

No less important than the religion of Cybele and Attis was the Greco-Egyptian religion of Isis and Osiris. Isis and Osiris are both ancient Egyptian gods, whose worship, in modified form, was carried over first into the Greek kingdom of the Ptolemies, and thence into the remotest bounds of the Roman Empire. The myth which concerns these gods is reported at length in Plutarch's treatise, "Concerning Isis and Osiris." Briefly it is as follows: Osiris, the brother and husband of Isis, after ruling in a beneficent manner over the Egyptians, is plotted against by his brother Typhon. Finally Typhon makes a chest and promises to give it to any one who exactly fits it. Osiris enters the chest, which is then closed by Typhon and thrown into the Nile. After a search, Isis finds the chest at Byblos on the coast of Phœnicia, and brings it back to Egypt. But Typhon succeeds in getting possession of the body of Osiris and cuts it up into fourteen parts, which are scattered through Egypt. Isis goes about collecting the parts. Osiris becomes king of the nether world, and helps his son Horus to gain a victory over Typhon.

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.

But it is the mysteries which arouse the greatest interest, especially because of the precious source of information about them which is found in the eleventh book of the Metamorphoses of Apuleius (second century after Christ). In this book, although the secrets of the mysteries themselves are of course not revealed, Apuleius has given a more complete and orderly account of the events connected with an initiation than is to be found anywhere else in ancient literature. The hero Lucius is represented first as waiting for a summons from the goddess Isis, which comes with miraculous coincidence independently to him and to the priest who is to officiate in his initiation. Then Lucius is taken into the temple and made acquainted with certain mysterious books, and also washes his body at the nearest baths. This washing has as little as possible the appearance of a sacrament; evidently it was not intended to produce "regeneration" or anything of the sort.[150] The purpose of it seems to have been cleanliness, which was naturally regarded as a preparation for the holy rite that was to follow. There follows a ten days' period of fasting, after which the day of initiation arrives. Lucius is taken into the most secret place of the temple. Of what happens there he speaks with the utmost reserve. He says, however: "I came to the limits of death, and having trod the threshold of Proserpine and been borne through all the elements I returned; at midnight I saw the sun shining with a bright light; I came into the presence of the upper and nether gods and adored them near at hand."[151] It is often supposed that these words indicate some sort of mysterious drama or vision, which marked the death of the initiate, his passage through the elements, and his rising to a new life. But certainly the matter is very obscure. The next morning Lucius is clothed with gorgeous robes, and is presented to the gaze of the multitude. Apparently he is regarded as partaking of the divine nature. Two other initiations of Lucius are narrated, one of them being an initiation into the mysteries of Osiris, as the first had been into the mysteries of Isis. But little is added by the account of these later experiences, and it has even been suggested that the multiplication of the initiations was due to the self-interest of the priests rather than to any real advantage for the initiate.

Similar in important respects to the Egyptian Osiris was the Adonis of Phœnicia, who may therefore be mentioned in the present connection, even though little is known about mysteries connected with his worship. According to the well-known myth, the youth Adonis, beloved by Aphrodite, was killed by a wild boar, and then bemoaned by the goddess. The cult of Adonis was found in various places, notably at Byblos in Phœnicia, where the death and resurrection of the god were celebrated. With regard to this double festival, Lucian says in his treatise "On the Syrian Goddess": "They [the inhabitants of Byblos] assert that the legend about Adonis and the wild boar is true, and that the facts occurred in their country, and in memory of this calamity they beat their breasts and wail every year, and perform their secret ritual amid signs of mourning through the whole countryside. When they have finished their mourning and wailing, they sacrifice in the first place to Adonis, as to one who has departed this life: after this they allege that he is alive again, and exhibit his effigy to the sky."[152] The wailing for Adonis at Byblos is similar to what is narrated about the worship of the Babylonian god Tammuz. Even the Old Testament mentions in a noteworthy passage "the women weeping for Tammuz" (Ezek. viii. 14). But the Tammuz-worship does not seem to have contained any celebration of a resurrection.