Middle Persian

Middle Persian, also called Pahlavi, was the official language of the Sasanian Empire from the third through seventh centuries CE, belonging to the Western Iranian branch of the Indo-Iranian family and standing as the direct linguistic ancestor of Modern Persian, though written in a notoriously difficult script derived from Aramaic that used numerous Aramaic words, called heterograms, as fixed spellings for entirely different Persian words to be read aloud, a convention that makes Pahlavi texts unusually challenging for modern readers to decipher without specialized training. Middle Persian became the primary language of an extensive Zoroastrian theological and legal literature composed after Avestan itself had ceased to be understood except by specialist priests, since Pahlavi allowed Zoroastrian scholars and clergy of the Sasanian period to interpret, translate and systematize the older Avestan scripture in a language they and their audience could actually read and discuss fluently.

Following the seventh-century Arab Muslim conquest of Persia, Middle Persian gradually gave way to New Persian, written in a modified Arabic script and heavily influenced by Arabic vocabulary, though Zoroastrian religious communities in Iran and India continued producing Pahlavi religious literature for centuries afterward.

The Bundahishn, meaning primal creation, is a major Zoroastrian cosmological text composed in Middle Persian, drawing on and synthesizing older Avestan material now lost in its original form, to describe Zoroastrian cosmogony, the cosmic struggle between the forces of Ahura Mazda and the destructive spirit Angra Mainyu, and the structure of the created world in extensive systematic detail, making it one of the most important surviving sources for reconstructing developed Sasanian-era Zoroastrian theology.

Middle Persian also produced the Zand, an extensive genre of interpretive commentary and translation on Avestan scripture, since by the Sasanian period few if any Zoroastrians could understand Avestan directly without such interpretive assistance, a situation historians of religion compare to the role Aramaic Targums played in helping Jewish communities access Hebrew scripture once Aramaic had displaced Hebrew as an everyday spoken language. Zoroastrian priests in both Iran and among the Parsi community of India continued producing and studying Pahlavi religious texts for centuries after the Arab conquest, preserving a substantial theological literature that modern Zoroastrian studies scholarship continues to draw upon heavily today.