"since the days of the Median Magi"

According to Herodotus’ The Histories (completed c. 440 BCE) the Magi were the sixth tribe of the Medians (until the unification of the Persian empire under Cyrus the Great, all Iranians were referred to as "Mede" or "Mada" by the peoples of the Ancient World), who appear to have been the priestly caste of the Mesopotamian-influenced branch of Zoroastrianism today known as Zurvanism, and who wielded considerable influence at the courts of the Median emperors.