Owing to their common origin, Iranian and Indo-Aryan religions are very similar.
From a comparative study of both groups, it is possible to reconstruct, in general features, the early forms of Iranian religion for which there is no direct documentation.
The remains of Achaemenian architecture and art, by far the most important of the material sources, provide abundant evidence of imperial articulation of religious symbols and show a thorough dependence on Middle Eastern precedents. These people were originally seminomadic pastoralists whose chief economic base was cattle, primarily bovines but also sheep and goats.(“nobles”) migrated from the steppes down into the Middle East, the Iranian plateau, and the northwestern part of the Indian subcontinent. They bred horses, which they used for riding and pulling chariots in warfare and sport.It is not at all clear how rigidly their society was originally segmented.There were specialists in religious matters, and men who could afford horses and chariots were reckoned as warriors and leaders.The main indigenous sources are the Achaemenian royal inscriptions in the Old Persian language (with Akkadian, Elamite, and Aramaic translations) and the ), for the most part eloquent pieces of propaganda, are rich in references to religion.
In addition to the information they contain, they have the great advantage of being fixed in time and place.
Among female deities the Earth, Spantā Aramati, and the sacred river, Ardvī Sūrā, were most prominent. Originally confined to ideas of social and natural order opposed by disorder and chaos, a dualistic ideology came to permeate all aspects of life.
The pantheon was divided between the gods and demons.
Apart from the Achaemenian inscriptions, there is no secure evidence that religious compositions were reduced to writing until the late Arsacid or early Sāsānian periods.
Thus, unlike the other religions of the Middle East, the Iranian religions had no written texts in the ancient period.
Ancient Iranian religion, diverse beliefs and practices of the culturally and linguistically related group of ancient peoples who inhabited the Iranian plateau and its borderlands, as well as areas of Central Asia from the Black Sea to Khotan (modern Hotan, China).