If “conversion” means to discard one’s own ancestral religion and to adopt an alien religion, then conversion is unknown in the Avesta, in the Zoroastrian religion, and in ancient Iranian history.

During the long and chequered history, the ancient Iranian rulers never adopted a policy of proselytization. On the contrary, the Iranian rulers have become famous in history for their liberal administration and liberal religious policy. They granted freedom of religion, belief, and worship to the subject peoples. This is too well known to detain us here particularly in connection with the Achaemenian and Parthian emperors. Some explanation, however, in connection with the Sasanian emperors is necessary.

LIBERAL RELIGIOUS POLICY
. The Iranians had come in contact with the Jewish people in very remote periods. During the Achaemenian times the Jews were an influential people in Iran. During that period the Greeks had also come in contact with the Iranians. During the Parthian period, the Jews, the Greeks, the Romans, and the Buddhists had settled in Iran. In Sasanian times, the Jews and Christians had their colonies, settlements, and religious institutions in Iran, and they were managing their own civic and religious affairs. Christianity came to Iran and Armenia about the beginning of the fourth century;
and since then the Christians were living peacefully in Iran enjoying political and religious freedom.

Thus Encyclopaedia of Religion and Ethics 11, p. 203 records:
“Christianity spread widely and was well organized in the Persian Empire under the Sasanians, specially in the Nestorian form. At the moment of the Musalman invasion it counted seven metropolitan provinces and 80 bishoprics, stretching from Armenia to India. Not infrequently Christians enjoyed high favour at the court, especially during the great reign of the first Chosroes.”

Dr Palon Ichaporia