Avestan: The Sacred Language of Zoroastrianism

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.