The Zoroastrian Scriptures are composed of three parts: the Avesta (6 letters), the Zend (4 letters), and the Zendavesta (10 letters). The Avesta is a collection of sacred texts written in an ancient Iranian language, and it includes the Gathas, which are hymns believed to have been composed by the prophet Zoroaster. The Zend is a commentary on the Avesta, and the Zendavesta is a combination of the Avesta and the Zend. Together, these three parts form the Zoroastrian Scriptures, which are the primary source of religious authority for Zoroastrians.