As the Parsis are the ruins of a people, so are their sacred books the ruins of a religion. There has been no other great belief in the world that ever left such poor and meagre monuments of its past splendor. Yet great is the value which that small book, the "Avesta," and the belief of that scanty people, the Parsis, have in the eyes of the historian and theologian, as they present to us the last reflex of the ideas which prevailed in Iran during the five centuries which preceded and the seven which followed the birth of Christ, a period which gave to the world the Gospels, the Talmud, and the Qur'ân. Persia, it is known, had much influence on each of the movements which produced, or proceeded from, those three books; she lent much to the first heresiarchs, much to the Rabbis, much to Mohammed. By help of the Parsi religion and the "Avesta," we are enabled to go back to the very heart of that most momentous period in the history of religious thought, which saw the blending of the Aryan mind with the Semitic, and thus opened the second stage of Aryan thought. Inquiries into the religion of ancient Persia began long ago, and it was the old enemy of Persia, the Greek, who first studied it. Aristotle, Hermippus, and many others wrote of it in books of which, unfortunately, nothing more than a few fragments or merely the titles have come down to us. We find much valuable information about it, scattered in the accounts of historians and travellers, extending over ten centuries, from Herodotos down to Agathias and Procopius (from B.C. 450 to A.D. 550). The clearest and most faithful account of the Dualist doctrine is found in the treatise _De Iside et Osiride_, ascribed to Plutarch. But Zoroastrianism was never more eagerly studied than in the first centuries of the Christian era, though without anything of the disinterested and almost scientific curiosity of the earlier times. Religious and philosophic sects, in search of new dogmas, eagerly received whatever came to them bearing the name of Zoroaster. As Xanthos the Lydian, who is said to have lived before Herodotos, had mentioned Zoroastrianism, there came to light, in those later times, scores of oracles, styled "Oracula Chaldaïca sive Magica," the work of Neo-Platonists who were but very remote disciples of the Median sage. As his name had become the very emblem of wisdom, they would cover with it the latest inventions of their ever-deepening theosophy. Zoroaster and Plato were treated as if they had been philosophers of the same school, and Hierocles expounded their doctrines in the same book. Proclus collected seventy Tetrads of Zoroaster and wrote commentaries on them; but we need hardly say that Zoroaster commented on by Proclus was nothing more or less than Proclus commented on by himself. Prodicus, the Gnostic, possessed secret books of Zoroaster; and, upon the whole, it may be said that in the first centuries of Christianity, the religion of