information:classification, structural:summarization
Classical antiquity

Zoroastrianism enters recorded history in the mid-5th century BCE. Herodotus ' The Histories (completed c. 440 BCE) includes a description of Greater Iranian society with what may be recognizably Zoroastrian features, including exposure of the dead.

The Histories is a primary source of information on the early period of the Achaemenid era (648–330 BCE), in particular with respect to the role of the Magi. According to Herodotus, the Magi were the sixth tribe of the Medes (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) and wielded considerable influence at the courts of the Median emperors.

Following the unification of the Median and Persian empires in 550 BCE, Cyrus the Great and later his son Cambyses II curtailed the powers of the Magi after they had attempted to sow dissent following their loss of influence. In 522 BCE, the Magi revolted and set up a rival claimant to the throne. The usurper, pretending to be Cyrus' younger son Smerdis, took power shortly thereafter. Owing to the despotic rule of Cambyses and his long absence in Egypt, "the whole people, Persians, Medes and all the other nations" acknowledged the usurper, especially as he granted a remission of taxes for three years.

Darius I and later Achaemenid emperors acknowledged their devotion to Ahura Mazda in inscriptions, as attested to several times in the Behistun inscription and appear to have continued the model of coexistence with other religions. Whether Darius was a follower of the teachings of Zoroaster has not been conclusively established as there is no indication of note that worship of Ahura Mazda was exclusively a Zoroastrian practice.

According to later Zoroastrian legend (Denkard and the Book of Arda Viraf), many sacred texts were lost when Alexander the Great 's troops invaded Persepolis and subsequently destroyed the royal library there. Diodorus Siculus 's Bibliotheca historica, which was completed c. 60 BCE, appears to substantiate this Zoroastrian legend. According to one archaeological examination, the ruins of the palace of Xerxes I bear traces of having been burned. Whether a vast collection of (semi-)religious texts "written on parchment in gold ink", as suggested by the Denkard, actually existed remains a matter of speculation.

Alexander's conquests largely displaced Zoroastrianism with Hellenistic beliefs, though the religion continued to be practiced many centuries following the demise of the Achaemenids in mainland Persia and the core regions of the former Achaemenid Empire, most notably Anatolia, Mesopotamia, and the Caucasus. In the Cappadocian kingdom, whose territory was formerly an Achaemenid possession, Persian colonists, cut off from their co-religionists in Iran proper, continued to practice the faith of their forefathers; and there Strabo, observing in the first century BCE, records (XV.3.15) that these "fire kindlers" possessed many "holy places of the Persian Gods", as well as fire temples. Strabo further states that these were "noteworthy enclosures; and in their midst there is an altar, on which there is a large quantity of ashes and where the magi keep the fire ever burning." It was not until the end of the Parthian Empire (247 BCE – 224 CE) that Zoroastrianism would receive renewed interest.