Paganism is essentially tolerant, and the Romans always extended a full measure of this toleration to the religions of the nations they conquered. The early custom of transferring to Rome the tutelary divinity of any conquered city in the vicinity is a practical expression of the view that any addition to the Roman pantheon (which had begun to grow into a Græco-Roman pantheon by the admittance of Apollo and the Sibyls and had actually been such since the war with Hannibal) must be regarded simply as an addition to the divine patrons of Rome. In the main this view was adhered to under the empire, although Augustus formulated more definitely the idea of a Roman state religion and closed the circle of gods to whom worship was due on the part of the state. But we have evidence of the spirit of tolerance and the capacity for assimilation characteristic of the age in the wide dissemination of the Egyptian cults of Isis and Serapis, especially in the upper ranks of society, and still more in the worship--deep rooted among the masses and spread abroad over the greatest part of the earth--of the Persian Mithras, whom Diocletian and his co-regents praised in the great Danubian camp of Caruntum as the patron of their dominion. Even the Phœnician gods of Africa and the Celtic gods of Gaul and the Danube provinces were allowed to survive by identification with Roman divinities of a somewhat similar character, and in the outlandish surnames bestowed upon the latter; although the names of the great Celtic divinities disappear from the monuments--a matter in which the government undoubtedly had a hand. So many barbarians, says Lucian the scoffer, have made their way into Olympus that they have ousted the old gods from their places, and ambrosia and nectar have become scanty by reason of the crowd of topers; and he makes Zeus resolve upon a thorough clearance, in order unrelentingly to thrust forth from Olympus all who could not prove their title to that divine abode, even though they had a great temple on earth and there enjoyed divine honours. In view of the lengths to which the Romans carried the principle of giving free course to every religion within the empire so long as its professors did not come into conflict with the government officials or tend to form hotbeds of political intrigue, such as were the schools of the Druids, how did it come to pass that the Christian religion, and to a less extent the Jewish religion also, were assailed as hostile and dangerous to the state?