The Vendidad is the Zoroastrian book of laws that was supposed to have been authored, if not written down, roughly around the time of Christ. The content, though, seems quite ancient. There is very little in the Vendidad that suggests that it was written for a civilized (urban) people, or even a warring people; yet, it is supposed to have been authored after Iran had been civilized for over 600 years. It is because of the ancient character of the content that I’m inclined to believe it retained much from an older, primitive tradition.

Reading the Vendidad, one might nearly guess that the supposed author was aware of little more than his own tribe. There’s nothing in the Vendidad about national or intertribal government, kings, or even warfare, though the existence of unbelievers is acknowledged. There are several passages that indicate some discrimination against unbelievers; for instance, murdering an unbeliever does not appear to be regarded as a crime (as in Judaism, perhaps to distinguish murder from warfare), and it also seems that an unbeliever could be absolved of some crimes by converting to Mazdaism.

There are also indications that Mazdean law does not apply to unbelievers, and that would seem to be corroborated by history. The Parthian Empire was evidently a relatively tolerant, loosely-organized empire, and though the Parthians’ Sasanian (Sassanid) successors were quite strict with regard to treason, heresy, and apostasy, they appear to have sometimes permitted Jews and Christians to live somewhat autonomously under their reign. It is thought that the Sasanians were the first rulers to apply what became known as the “millet” system, wherein each recognized religious group would enforce its own laws internally.

“… under the early Sasanians much of the groundwork for the future was established. For example the authority over political and economic affairs of the heads of various religious minorities, famous as the millet system of the much later Ottoman Empire, seems to have been organized by the early Sasanians, as well as the tax system applied to minorities.”

The Seleucid, Parthian and Sasanian periods
Edited by Ehsan Yar-Shater
The Cambridge History of Iran
Page 132

‘It was likewise under Sassanid rule that the first agreement which can properly be called by the name of “millet” was concluded.’

Religion and Nationality
Werner J. Cahnman

“In 410 AD, during the rule of Yazgard I (399-420), Christians were recognized as a millet, or separate religious community, and were protected as such within the organization of the Sassanid Empire. The Sassanid law recognized that the Head of the Christian millet was responsible for upholding discipline within the millet and that the state gave formal backing and recognition to the Head.”

The Christians of Lebanon
Political Rights in Islamic Law
By David D. Grafton
Page 20

The millet system of Yazdagird I, the enlightened rule of other Sassanid kings like Hormizd IV, and the open rule of the Parthians were, in a sense, continuations of a more ancient tradition of interfaith tolerance; established a millennium earlier by Cyrus the Great.

Unfortunately, this and other gestures of Royal toleration were more than equaled by waves of persecution, usually driven by the Zoroastrian priesthood. This is no surprise, for the people most invested in the status quo (the priesthood and aristocracy), as well as the people that must have truly believed the doctrines of traditional Zoroastrianism would have been in natural opposition to religions like Christianity, Mazdakism, and Manichaenism. Irreconcilable beliefs about eternal salvation and damnation are bound to fall into conflict before long.

Still, the situation was not simple. Persecution against Manichaenism, for instance, only flared up after 30 years of royal support had allowed the young faith to flourish. Persecution against Christians, for their part, was often a reaction against Christian expansion efforts and refusal to respect the gods of other peoples.

The question I am attempting to find an answer for is: did Zoroastrianism help or hurt the situation? I am inclined to believe the latter. The dominant traditionalism was too strong to permit toleration for long, in spite of more enlightened aspects of the faith. It was typically the kings who sought tolerance, perhaps realizing a modest tolerance to be in the best interests of the Empire.