But, however absorbing this important problem may be, we could not think of going into it, even briefly, in these studies on Roman paganism. In the Latin world the question assumes much more modest proportions, and its aspect changes completely. Here Christianity spread only after it had outgrown the embryonic state and really became established. Moreover like Christianity the Oriental mysteries at Rome remained for a long time chiefly the religion of a foreign minority. Did any exchange take place between these rival sects? The silence of the ecclesiastical writers is not sufficient reason for denying it. We dislike to acknowledge a debt to our adversaries, because it means that we recognize some value in the cause they defend, but I believe that the importance of these exchanges should not be exaggerated. Without a doubt certain ceremonies and holidays of the church were based on pagan models. In the fourth century Christmas was placed on the 25th of December because on that date was celebrated the birth of the sun (_Natalis Invicti_) who was born to a new life each year after the solstice.[3] 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 {xviii} the world, it imposed itself even on its enemies. The Phrygian priests of the Great Mother openly opposed their celebration of the vernal equinox to the Christian Easter, and attributed to the blood shed in the taurobolium the redemptive power of the blood of the divine Lamb.[4] 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 modern 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. {xix}