Accordingly, as the canonization of the scripture took place long after the Achaemenian period, the lack of references to identifiable Achaemenian realia makes the Avesta an elusive source for the religion of Achaemenian Iran, and Persia. The Younger Avestan Ahura Mazda is "primus" only in respect of his name occurring in the texts much more often than those of the other gods; the compiler insistently represents Zoroaster's sole god as approving of the polytheism the prophet had proscribed, with the result that Zoroaster himself is presented as a polytheist. The most important god of pagan origin, Mithra maintained his great popularity down through Iranian history. A comparison of the Avestic demonological data with that of the Vedas shows that the Iranians inherited the foundations of their beliefs concerning malign supernatural beings from Indo-Iranian times. The Pahlavi books have another series of oppositions of demons to the Amesha Spentas. Evidence is lacking for religion under the predecessors of Darius I.