Avestan

Avestan is the ancient Iranian language in which the Avesta, Zoroastrianism's core scripture, was composed, belonging to the Indo-Iranian branch of the Indo-European family and standing in a close grammatical relationship to Vedic Sanskrit that historical linguists treat as one of the clearest surviving demonstrations of a shared Indo-Iranian ancestor language, given the two languages' strikingly similar meter, vocabulary and specific ritual terminology despite their geographic separation between ancient Iran and India.

Avestan exists in two distinguishable historical layers, Old Avestan, the more archaic form associated with the Gathas traditionally attributed to Zoroaster himself, and Younger Avestan, a somewhat later form in which the bulk of the remaining Avesta was composed, and Avestan as a spoken vernacular disappeared entirely in antiquity, surviving only as a fixed liturgical language preserved through oral priestly transmission for many centuries before eventually being written down using an adapted Middle Persian script developed specifically for accurate Avestan recitation. Avestan's script itself, adapted specifically from a Middle Persian writing system and expanded with additional characters to capture Avestan's distinct sounds precisely, was developed relatively late, likely under the Sasanian Empire, specifically to fix correct pronunciation for a liturgical tradition that had already been recited orally for well over a millennium by that point.

The Avesta's oldest portion, the Gathas, seventeen hymns traditionally attributed directly to the prophet Zoroaster himself and composed in the more archaic Old Avestan register, were preserved through a specialized priestly oral tradition for well over a thousand years before being committed to writing, comparable in its precision and religious motivation to the Vedic Sanskrit recitation tradition preserving the Rigveda across a similarly vast span of time without writing. Zoroastrian priests, mobeds, continue to recite Avestan liturgical texts today in Zoroastrian communities in Iran and among the Parsi community of India, descended from Zoroastrians who fled Iran following the seventh-century Muslim conquest, even though almost no modern practitioner speaks Avestan as anything but a memorized liturgical register entirely separate from everyday Persian or Gujarati speech.

The Bundahishn, a later Zoroastrian cosmological text, was composed not in Avestan itself but in Middle Persian, drawing on and interpreting older Avestan material, illustrating how Avestan's own scriptural authority persisted even as the practical theological and interpretive work increasingly moved into more recent Iranian languages that later generations of priests and scholars could actually read fluently.