However, he was sent back to Persis to keep watch over his eldest son, Darius, whom Cyrus, after a dream, suspected of considering treason.

[7] Ammianus Marcellinus[2] makes him a chief of the Magians, and tells a story of his studying in India under the Brahmins, an event that would correspond to the Achaemenid conquest of the Indus Valley:[8] "Hystaspes, a very wise monarch, the father of Darius.

Who while boldly penetrating into the remoter districts of upper India, came to a certain woody retreat, of which with its tranquil silence the Brahmans, men of sublime genius, were the possessors.

From their teaching he learnt the principles of the motion of the world and of the stars, and the pure rites of sacrifice, as far as he could; and of what he learnt he infused some portion into the minds of the Magi, which they have handed down by tradition to later ages, each instructing his own children, and adding to it their own system of divination".In ancient sources, Hystaspes is sometimes considered as identical with Vishtaspa (the Avestan name for Hystapes), an early patron of Zoroaster.

Historian Lloyd Llewellyn-Jones suggests that the Takht-e Gohar, previously attributed as the tomb of Cambyses II, was actually that of Hystaspes.