Sasanian Avesta

The Sasanian Avesta or Great Avesta refers to the anthology of Zoroastrian literature produced during the Sasanian period. They are said to have been written down during the reign of Khosrow. Most of this work is now lost, but its content and structure can be reconstructed from references found in a number of texts from the 9th century onward.

Compared to the extant Avesta, the Sasanian Avesta was much larger and organized into 21 distinct volumes called nasks (Avestan: naska; Middle Persian: nask, 'bundle'). Of those, only one is preserved in its entirety, while others are either lost or only preserved in fragments.