Zoroastrian scripture survived for centuries in a language nobody spoke
Avestan, the sacred language of Zoroastrianism, died out long before anyone wrote it down. Priests carried its hymns by memory for centuries, and when an alphabet was finally invented for them in Sasanian Persia, it had 53 letters so that every sound of the prayers could be captured precisely. Nobody knows what its speakers called it.
Avestan is an Iranian branch of the Indo-European family. Its older form, Old or Gathic Avestan, is strikingly close to Vedic Sanskrit in grammar and vocabulary, a sign that not much time had passed since both split from their shared Indo-Iranian parent. Younger Avestan resembles Old Persian more, and the two old forms are best seen as related dialects rather than one straight line of descent. Along with Old Persian, it is one of only two Old Iranian languages known from long texts; Median and early Scythian survive only as scattered words and names.
Its name is borrowed from the Avesta, the written collection of its texts, much as Vedic is named after the Vedas. The speakers called themselves Arya, Iranians, but never gave the language a name of its own. Older books sometimes call it Zend, a mistake arising because Zend really means the Middle Persian commentaries often bound together with the scripture.
Dating it has shifted. When Zarathustra was placed in the 6th century BCE, Old Avestan looked like a language of the early Achaemenid era. Recent scholarship pushes it earlier, because the Gathas closely resemble the Rigveda of the second half of the second millennium BCE, and the Younger texts show no trace of western Persian or Median influence. Place names in those later texts point to eastern Greater Iran, roughly today's Afghanistan and Tajikistan with parts of neighbouring countries, and the Yaz archaeological culture, which left no graves consistent with open-air exposure of the dead, is a leading candidate for its speakers.
The texts froze in stages, becoming fixed liturgy recited by communities that no longer spoke the language, and native Persian speakers left traces in pronunciation. The script, drawn largely from cursive Pahlavi with vowels adapted from Greek letters, is written right to left. Much of the literature was still lost after the 10th century CE, and surviving manuscripts carry copying errors.
Source: Avestan
