Magiam opinionum insignium auctor amplissimus Plato hagistiam esse verbo mystico docet, divinorum incorruptissimum cultum, cuius scientiae saeculis priscis multa ex Chaldaeorum arcanis Bactrianus addidit Zoroastres, deinde Hystaspes rex prudentissimus Darei pater. qui cum superioris Indiae secreta fidentius penetraret, ad nemorosam quandam venerat solitudinem, cuius tranquillis silentiis praecelsa Brachmanorum ingenia potiuntur, eorumque monitu rationes mundani motus et siderum, purosque sacrorum ritus (quantum colligere potuit) eruditus, ex his, quae didicit, aliqua sensibus magorum infudit, quae illi cum disciplinis praesentiendi futura, per suam quisque progeniem, posteris aetatibus tradunt.
(Ammianus Marcellinus, Res Gestae 23.6.32-33)
According to Plato, the most eminent author of lofty ideas, magic, under the mystic name of hagistia, is the purest worship of the gods. To the science of this, derived from the secret lore of the Chaldaeans, in ages long past the Bactrian Zoroaster made many contributions, and after him the wise king Hystaspes, the father of Darius. When Zoroaster had boldly made his way into the unknown regions of Upper India, he reached a wooded wilderness, whose calm silence the lofty intellects of the Brahmins control. From their teaching he learned as much as he could grasp of the laws regulating the movements of the earth and the stars, and of the pure sacrificial rites. Of what he had learned he communicated something to the understanding of the Magi, which they, along with the art of divining the future, hand on from generation to generation to later times. (tr. John C. Rolfe)