Ancient Iranian religion was strongly connected. Beginning in the early 10th-century BC, the ancient Iranian religion was gradually displaced by Zoroastrianism, which contains many essential aspects of its predecessor. The sources on ancient Iranian religion, though limited, consist of textual and material sources. The textual sources are both Iranian and non-Iranian. An important Iranian source is the Avesta, which are Zoroastrian sacred scriptures made in the Avestan. This is considered the principal source of knowledge on ancient Iranian religions. It is a collection of several texts that seems to have been over a large span of time by a variety of authors. These
Religion in Asia trying to destroy the creation of Mazda (asha), and good trying to sustain it. Mazda is not immanent in the world, and His creation is represented by the Amesha Spentas and the host of other Yazatas, through whom the works of God are evident to humanity, and through whom worship of Mazda is ultimately directed. The most important texts of the religion are those of the Avesta, of which a significant portion has been lost, and mostly only the liturgies of which have survived. The lost portions are known of only through references and brief quotations in the later works