Ancient Iranian religion was a set of ancient beliefs and practices of the Iranian peoples before the rise of Zoroastrianism. The religion closest to it was the historical Vedic religion that was practiced during the Vedic period. The major deities worshipped were Ahura Mazda and Mithra from Iran to Rome, but Atar was also worshipped, as names of kings and common public showing devotion to these three exist in most cases. Some sects, the precursors of the Magi, also worshipped Ahura Mazda, the chief of the Ahuras. With the rise of Zoroaster and his new, reformatory religion, Ahura Mazda became the principal deity, while the Daevas were relegated to the background. Many of the attributes and commandments of Varuna, called Fahrana in Median times, were later attributed to Ahura Mazda by Zoroaster.
The Iranian peoples emerged as a separate branch of the Indo-Iranians in the 2nd millennium BC, during which they came to dominate the Eurasian Steppe and the Persian Plateau. Their religion is derived from Iranian religions, and therefore shares many similarities with the Vedic religion of India. Although the Persian peoples left little written or material evidence of their religious practices, their religion is possible to reconstruct from scant Iranian, Babylonian and Greek accounts, similarities with Vedic and other Indo-European religions, and material evidence.
Prior to the Achaemenid period, the daivas were also commonly worshipped. The Achaemenid kings made it a state policy to destroy their shrines and vilify them. Old Iranian daiva occurs twice in Xerxes I's daiva inscription (XPh, early 5th century BCE). This trilingual text also includes one reference to a daivadana ("house of the daivas"), generally interpreted to be a reference to a shrine or sanctuary. In his inscription, Xerxes I records that "by the favor of Ahura Mazda I destroyed that establishment of the daivas and I proclaimed, 'The daivas thou shalt not worship!. This statement has been interpreted either one of two ways. Either the statement is an ideological one and daivas were gods that were to be rejected, or the statement was politically motivated and daivas were gods that were followed by (potential) enemies of the state..
Under the Achaemenids, Ahura Mazda received state patronage as the chief deity and the emperors became his representatives. Ahura Mazda was thus recognized as the creator of the world. Dualism was strongly emphasized and human nature was considered essentially good. The chief ritual of the ancient Iranians was the yasna, in which the deities were praised and the mind-altering drug hauma was consumed. This ritual was performed by a highly trained priestly class. Politics and religion under the Persian empires were strongly connected.
Beginning in the early 10th century BC, the ancient Iranian religions were gradually displaced by Zoroastrianism, which contains some aspects of its predecessor.
Sources The sources on ancient Iranian religion, though limited, consist of textual and material sources. The textual sources are both Iranian and non-Iranian.
Iranian sources
An important Iranian source is the Avesta, which are Zoroastrian sacred scriptures made in the Avestan language. This is considered the principal source of knowledge on ancient Iranian religions. It is a collection of several texts that seems to have been written over a large span of time by a variety of authors. These texts have been subjected to editings and redactions throughout their development. It is now the only extant fragment of what remained in the 9th century CE of the Avesta compiled in the Sasanian Empire by Khosrow I (6th century CE). Summaries of its content reveal that it was a huge collection containing texts not only in Avestan, but also in Pahlavi, which was the language of Zoroastrianism in the Sasanian Empire. Though the existing Avesta is dated quite recently, it contains information that is considerably older. The Gathas ("Songs") of the Prophet Zoroaster, the Yasnas and much of the Yashts are considered among the oldest. The Gathas includes expressions of the religious vision of Zoroaster, which in many ways is a reinterpretation of the ancient Iranian religious principles. The Yashts are a collection of verses dedicated to various deities. These verses are mostly related to Zoroastrian terminology and ideas, but have little relation to anything specifically Zoroastrian. The gods invoked are basically the pre-Zoroastrian gods of the Iranian peoples. There is little agreement on when Zoroaster lived, but most scholars agree that he lived somewhere between 1200 and 600 BC. Dating the Yashts is similarly difficult, but it is likely that they were redacted (not necessarily composed) initially in the 5th century BC.
Another Iranian source are royal inscriptions of the Achaemenid Empire made in the Old Persian (with Akkadian, Aramaic and Elamite translations). These inscriptions, in particular those of Darius I and his son Xerxes I, contain many references to religion. The fact that these are fixed in time and place make them particularly useful.
Except from the Achaemenid inscriptions, there is no evidence that the Iranian religious compositions were written until the late Parthian or Sasanian period. This makes ancient Iranian religion the only major religion of the Middle East which has no written texts in the ancient period. The religious information was rather oral both in composition and transmission.
Non-Iranian sources The ancient Vedic Sanskrit literature of ancient India, which shares a common ancestor with Proto-Indo-Iranian paganism and predates the first Avestan scriptures by at least a few centuries, is perhaps the most important source. The earliest religious texts of the related Indo-Aryan peoples are indispensable for reconstructing the historical development of the ancient Iranian religion. The most important of these texts in this regard is the Rigveda. It is composed of more than 1,000 hymns dedicated to various deities.
Other non-Iranian sources are mostly Greek. The most important Greek source is Herodotus. Some Greek information on ancient Iranian religion is unreliable, due to being based on outright wrong information or on misunderstandings.
Material sources Material sources are rather limited and mostly confined to western Iran. The remains of Achaemenid architecture are the most important of these material sources. They provide a mass of evidence of imperial articulation of religious symbols and indicate a significant dependence on Middle Eastern precedents.
Origins
During the first half of the 2nd millennium BC, one group of Indo-Europeans migrated southwards from Central Asian Steppe into the Iranian plateau and the Indian subcontinent. These are known by scholars as the Indo-Iranians. They eventually branched out into the Indo-Aryan peoples and Iranian peoples. Because of their common origin, Iranian and Indo-Aryan religion is substantially similar. Through a comparative study of both groups one can reconstruct general features of Iranian religion for which there is no direct documentation.
The Iranian peoples were originally seminomadic pastoralists whose main economic base was herds, chiefly cattle but also goats and sheep. They excelled at breeding horses, which they used for riding and pulling chariots in sport and warfare. Exactly how rigid their society was is difficult to determine. The Iranian peoples were specialists in religious matters. Men who could afford chariots and horses were recognized as leaders and warriors.
By the creation of the Achaemenid Empire, a more rigid division of society into priests, nobles, farmers and artisans had developed. Society was heavily patriarchal, which was strongly reflected in religion. As the Iranian peoples settled the land they became more engaged in agriculture and sedentary life. During this process they were influenced by the indigenous populations. The religions of these peoples are completely unknown except from the elements they have left Iranian religion which have no parallel with other Indo-European religions.
Cosmology Cosmography The ancient Iranians believed in a cosmos which was a three-tiered structure. This structure consisted of the earth, the atmosphere, and the heaven above. Beyond heaven was the realm of Endless Lights while below the earth lay the realm of darkness and chaos. The earth rested on a cosmic ocean called the Varu-Karta. In the earth's centre was cosmic mountain Hara. Down the Hara flowed the river Ardvi.
The earth divided into six continents surrounding the central continent. The central continent was Khvaniratha, the locus of Airyanem Vaejah (land of the Aryans).
Creation
Ahura Mazda is the creator of heaven and earth. Beside Ahura Mazda is the ancient Indo-Iranian god Thvarshtar ("Artisan"). Thvarstar also appears under the name Spenta Mainyu ("the Beneficient Spirit") in Zoroaster's system of the Beneficent Immortals. In the creative aspect Thvarshtar functions in many ways as Ahura Mazda. In the Younger Avesta Spenta and the Gathas Mainyu is paired with the evil antagonist Angra Mainyu ("the Evil Spirit", Ahriman in Middle Persian). In later sources it is Ohrmazd (Middle Persian for Ahura Mazda) who is paired with Ahriman. The Avesta contains cryptic allusions to the creations of two antagonistic spirits.
It is Plutarch (De Iside et Osiride 47), who conducts the first discursive exposition of world creation by two spirits. Plutarch describes the Persians as telling mythical tales about Oromazes (i.e., Ahura Mazda), who is born from light, and Areimanios (i.e., Ahriman), who is born from gloom, engaging in a war against each other. This dualistic idea of two primordial spirits, which Zoroaster calls twins, is an early Indo-European concept. Reconstruction indicates that primordial twins that existed before the creation of the world, came into conflict. One was named "Man" (Iranian *Manu', meaning "man"), the other was named "Twin" (Iranian Yama, Avestan Yima). After Man killed Yima he used his dismembered body to fashion the world. He used the flesh for the earth, the bones for the mountains, the skull for the sky, etc. In a different Iranian variant of the myth, Yama is the first mortal and the first ruler. His rule is described as a golden age in which there is no hot or cold, no death or old age, etc. When falsehood enters Yama's speech this golden age comes to an end. The Khvarenah "Royal Glory" departs from Yama and seeks refuge in the cosmic sea. Azhi Dahaka "Dahaka the Snake", a serpentine tyrant, then overthrows Yama. His rule ushers in a period of chaos, drought and ruin. Azhi is later defeated by the hero Θraētaona. Θraētaona establishes the legendary line of rulers called the Kayanian dynasty.
Myths Since all sources on Persian mythology, both from indigenous texts and classical authors, originated after the emergence of Zoroastrianism, it is difficult to distinguish between myths that are Zoroastrian innovations and those that are inherited. The fact that Zoroastrianism was heavily inspired by existing ideas and had adapted from previous Iranian religions makes the distinction difficult to discern. Like other ancient religions, Iranian religions did not have an organized collection of myths. Iranian myths are rather fragments from various stories that exhibit variations on common themes.