In the II and I millennia ВС, the native population of Iran adopted the cults of the Indo-European tribes who had recently arrived on the plateau. These cults, known generically by the term Mazdaism, were to develop along separate lines in different regions but most of them recognized a god called Ahura Mazda (or Ormazd). Very little information is available about this ancient past, which predates the Achaemenian period, and our present knowledge of these cults is based largely on the study and comparison of ancient Iranian and Indian oral traditions which much later were crystalised in oral form. Because of their common Aryan heritage, the Iranian cults show a close relationship with the ancient Indo-Aryan religion as it appears in the Vedas, particularly in the names and functions of the gods, and the division of society into three classes: priest, warrior and pastoralist-agriculturalist.
The Aryan religion was a polytheistic one which recognized a principal god, Ahura Mazda (Varuna in India), who was surrounded by a group of divinities known as the Amesa Spenta. The worship of these gods centred around two essential elements, fire and haoma. Fire, by nature sacred and purifying, remained a central element of Zoroastrianism, and is so today. Haoma is the equivalent of the Indian soma, an inebriating drink, honoured as an equal of the gods, which was used during sacrificial rites. The sacrifice of animals, usually of bulls, was one of the main rites associated with the worship of the gods in Mithraism.
Nowadays, the state religion of Iran is the Shi'i Ithna 'Ashari branch of Islam, though a number of Sunnis still reside in the country. In addition to various ethnic groups, there are also a number of religious minorities living in Iran. Zoroastrians, Jews and Christians are recognized as minorities by Article 13 of the Constitution, which guarantees them freedom of religion. The Bahai are not recognized as a valid religious minority, and have suffered not inconsiderable persecution. The Zoroastrians still practice the ancient pre-Islamic religion, whose origins go back to the beliefs of the Indo-European immigrants of the I millennium ВС and which was confirmed as the state religion under the Sassanians. After the Arab conquest and the arrival of Islam, the Zoroastrians were tolerated as a disarmed and defeated poulus paying heavy taxes. Christians and Jews, as People of the Book, or ahl al-kitab, were also made to pay the poll tax as a protected minority, ahl al-dhimma.
The Arab policy of religious tolerance towards non-Muslims living in the conquered territories provides them with a legal status within the Muslim community. This status was determined by a pact, or dhimma, said to exist between the two communities. According to this pact, non-Muslims accepted a subordinate position with certain social restrictions and the payment of tribute, in return for which they were guaranteed physical protection against their enemies, freedom of worship and a limited autonomy in the running of their community.