The Zend-Avesta, Part 1: The Vendidad (Sacred Books of the East, Vol. 4)

...[Zoroas]ter. 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 them¹; but we need hardly say that Zoroaster commented on by Proclus was nothing more or less than Proclus commented on by Proclus. Prodicus the Gnostic had secret books of Zoroaster²; and upon the whole it may be said that in the first centuries of Christianity, the religion of Persia was more studied and less understood than it had ever been before. The real object aimed at, in studying the old religion, was to form a new one.

Throughout the Middle Ages, nothing was known of Mazdaeism but the name of its founder, who from a Magus was converted into a magician and master of the hidden sciences. It was not until the Renaissance that real inquiry was resumed. The first step was to collect all the information that could be gathered from Greek and Roman writers. That task was undertaken and successfully completed by Barnabé Brisson³. A nearer approach to the original source was made in the following century by Italian, English, and French travelers in Asia. Pietro della Valle, Henry Lord, Mandelslo, Ovington, Chardin, Gabriel du Chinon, and Tavernier found Zoroaster's last followers in Persia and India, and made known their existence, their manners, and the main features of their belief to Europe. Gabriel du Chinon saw their books and recognized that they were not all written in the same language, their original holy writ being no longer understood except by means of translations and commentaries in another tongue.

¹ Fabricius, Graeca Bibliotheca, fourth ed. p. 309 seq.
² Clemens Alexandrinus, Stromata I. Cf. infra, III. 11, and Porphyrius, de vita Plotini, § 16.
³ 'De regio Persarum principatu libri tres,' Paris, 1590. The second book is devoted to the religion and manners of the ancient Persians.