Zoroastrianism emerged out of a common prehistoric Indo-Iranian religious system dating back to the early 2nd millennium BCE.According to Zoroastrian tradition, Zoroaster was a reformer who exalted the deity of Wisdom, Ahura Mazda, to the status of Supreme Being and Creator, while demoting various other deities and rejecting certain rituals.
Farvahar. Persepolis, Iran.
Although older, Zoroastrianism only enters recorded history in the mid-5th century BCE.Herodotus' The Histories (completed c. 440 BCE) includes a description of Greater Iraniansociety 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 i.101, 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. 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 (Herodotus iii. 68).
The Behistun Inscription, Iran.
According to the Behistun Inscription, pseudo-Smerdis ruled for seven months before being overthrown by Darius I in 521 BCE. The "Magi", though persecuted, continued to exist. A year following the death of the first pseudo-Smerdis (named Gaumata), a second pseudo-Smerdis (named Vahyazdāta) attempted a coup. The coup, though initially successful, failed. Whether Cyrus II was a Zoroastrian is subject to debate. It did, however, influence him to the extent that it became the non-imposing religion of his empire, and its beliefs later allowed Cyrus to free the Jews and allow them to return to Judea when the emperor took Babylon in 539 BCE. Darius I was a devotee of Ahura Mazda, as attested to several times in the Behistuninscription. However, whether he was a follower of Zoroaster has not been conclusively established, since devotion to Ahura Mazda was (at the time) not necessarily an indication of an adherence to Zoroaster's teaching. Darius I and later Achaemenid emperors, though acknowledging their devotion to Ahura Mazda in inscriptions, appear to have permitted religions to coexist. Nonetheless, it was during the Achaemenid period that Zoroastrianism gained momentum. A number of the Zoroastrian texts that today are part of the greater compendium of the Avesta have been attributed to that period. It was also during the later Achaemenid era that many of the divinities and divine concepts of proto-Indo-Iranian religion(s) were incorporated in Zoroastrianism, in particular those to whom the days of the month of the Zoroastrian calendar are dedicated. This calendar is still used today, a fact that is attributed to the Achaemenid period. Additionally, the divinities, or yazatas, are present-day Zoroastrian angels(Dhalla, 1938). Almost nothing is known of the status of Zoroastrianism under the Seleucids and Parthians, who ruled over Persia following Alexander the Great's invasion in 330 BCE. According to later Zoroastrian...