Albert de Jong, Regional Variation in Zoroastrianism: The Case of the Parthians

The Parthians are almost completely absent from historical overviews of Zoroastrianism, which in the Sasanian period was reworked by rulers to accomodate the kings' imperial ambitions and was utilized to legitimatize the reigning monarch. Today, basically we have only the Sasanian version of Zoroastrianism, which survived the Arab conquest. Despite this, it is certain that the Parthians were Zoroastrians, as note the Nisa ostraca and the Parthian parchment from Avroman, as well as the use of the Zoroastrian calendar, and there are indications that Zoroastrian practice had included the cult of divine images.