Later Zoroastrian tradition, recorded centuries afterward in the Denkard and associated with a figure called Tansar, credits Ardashir's reign with beginning a deliberate program of religious consolidation, gathering scattered Avestan material, standardizing priestly practice, and asserting that political and religious order were a single project, summarized in a phrase historians gloss as one king, one religion. A letter attributed to Tansar defending forced religious unification on these grounds survives in a later Arabic and then Persian recension, and its precise relationship to events of Ardashir's actual reign is debated: Mary Boyce, among others, treats it as reflecting genuine early Sasanian religious policy dressed in later literary form, while other historians read it more as Sasanian era ideology projected backward to legitimize a later state of affairs.
What is not seriously disputed is the outcome: by the end of the Sasanian period, Zoroastrianism held a position as imperial state religion, with royal patronage of fire temples, an increasingly organized priestly hierarchy, and eventually the redaction of the Avesta into something closer to the scripture later Zoroastrians inherited, a process tradition traces to a beginning under Ardashir even where the details of his own personal role remain harder to verify than the inscriptions of a figure like Kartir make possible for the following century.