IN November, 1905, the Collège de France honored the writer by asking him to succeed M. Naville in opening the series of lectures instituted by the Michonis foundation. A few months later the "Hibbert Trust" invited him to Oxford to develop certain subjects which he had touched upon at Paris. In this volume have been collected the contents of both series with the addition of a short bibliography and notes intended for scholars desirous of verifying assertions made in the text. The form of the work has scarcely been changed, but we trust that these pages, intended though they were for oral delivery, will bear reading, and that the title of these studies will not seem too ambitious for what they have to offer. The propagation of the Oriental religions, with the development of neo-Platonism, is the leading fact in the moral history of the pagan empire. May this small volume on a great subject throw at least some light upon this truth, and may the reader receive these essays with the same kind interest shown by the audiences at Paris and Oxford. The reader will please remember that the different chapters were thought out and written as lectures. They do not claim to contain a debit and credit account of what the Latin paganism borrowed from or loaned to the Orient. Certain well-known facts have been deliberately We wish to slight neither the interest nor the importance of that controversy, and it is not because it seemed negligible that we have not entered into it. By reason of their intellectual bent and education the theologians were for a long time more inclined to consider the continuity of the Jewish tradition than the causes that disturbed it; but a reaction has taken place, and to-day they endeavor to show that the church has borrowed considerably from the conceptions and ritualistic ceremonies of the pagan mysteries. In spite of the prestige that surrounded Eleusis, the word "mysteries" calls up Hellenized Asia rather than Greece proper, because in the first place the earliest Christian communities were founded, formed and developed in the heart of Oriental populations, Semites, Phrygians and Egyptians. Moreover the religions of those people were much farther advanced, much richer in ideas and sentiments, more striking and stirring than the Greco-Latin anthropomorphism. Their liturgy always derives its inspiration from generally accepted beliefs Certain vestiges of the religions of Isis and Cybele besides other polytheistic practices perpetuated themselves in the adoration of local saints. On the other hand as soon as Christianity became a moral power in All these facts constitute a series of very delicate problems of chronology and interrelation, and it would be rash to attempt to solve them en bloc. Probably there is a different answer in each particular case, and I am afraid that some cases must always remain unsolved. We may speak of "vespers of Isis" or of a "eucharist of Mithra and his companions," but only in the same sense as when we say "the vassal princes of the empire" or "Diocletian's socialism." These are tricks of style used to give prominence to a similarity and to establish a parallel strongly and closely. A word is not a demonstration, and we must be careful not to infer an influence from an analogy. Preconceived notions are always the most serious obstacles to an exact knowledge of the past. Some modem writers, like the ancient Church Fathers, are fain to see a sacrilegious parody inspired by the spirit of lies in the resemblance between the mysteries and the church ceremonies. Other historians seem disposed to agree with the Oriental priests, who claimed priority for their cults at Rome, and saw a plagiarism of their ancient rituals in the Christian ceremonies. It would appear that both are very much mistaken. Resemblance does not necessarily presuppose imitation, and frequently a similarity of ideas and practices must be explained by common origin, exclusive of any borrowing. On the other hand, we find similar conceptions in Christianity. The society of the faithful--the term is still in use--is the "Church Militant." During the first centuries the comparison of the church with an army was carried out even in details; the baptism of the neophyte was the oath of fidelity to the flag taken by the recruits. Christ was the "emperor," the commander-in-chief, of his disciples, who formed cohorts triumphing under his command over the demons; the apostates were deserters; the sanctuaries, camps; the pious practices, drills and sentry-duty, and so on. If we consider that the gospel preached peace, that for a long time the Christians felt a repugnance to military service, where their faith was threatened, we are tempted to admit a priori an influence of the belligerent cult of Mithra upon Christian thought. This conception of life, especially of religious life, was therefore very popular from the beginning of our era. It was manifestly prior both to Christianity and to Mithraism. It developed in the military monarchies of the Asiatic Diadochi. Here the soldier was no longer a citizen defending his country, but in most instances a volunteer bound by a sacred vow to the person of his king. In the martial states that fought for the heritage of the Achemenides this personal devotion dominated or displaced all national feeling. We know the oaths taken by those subjects to their deified kings. They agreed to defend and uphold them even at the cost of their own lives, and always to have the same friends and the same enemies as they; they dedicated to them not only their actions and words, but their very thoughts. Their duty was a complete abandonment of their personality in favor of those monarchs who were held the equals of the gods. The sacred militia of the mysteries was nothing but this civic were developed there, and it is there we must look for the key to enigmas still unsolved. It is true that at present nothing is more obscure than the history of the religions that arose in Asia when Greek culture came in contact with barbarian theology. It is rarely possible to formulate satisfactory conclusions with any degree of certainty, and before further discoveries are made we shall frequently be compelled to weigh contrasting probabilities. We must frequently throw out the sounding line into the shifting sea of possibility in order to find secure anchorage. But at any rate we perceive with sufficient distinctness the direction in which the investigations must be pursued. It is our belief that the main point to be cleared up is the composite religion of those Jewish or Jewish-pagan communities, the worshipers of Hypsistos, the Sabbatists, the Sabaziasts and others in which the new creed took root during the apostolic age. In those communities the Mosaic law had become adapted to the sacred usages of the Gentiles even before the beginning of our era, and monotheism had made concessions to idolatry. Many beliefs of the ancient Orient, as for instance the ideas of Persian dualism regarding the infernal world, arrived in Europe by two roads, the more or less orthodox Judaism of the communities of