Sacred scripture of Zoroastrianism. It consists of five parts: Gathas (poems written by Zoroaster), Visparat (homages to spiritual leaders), Vendidad (legal and medical doctrine), Yashts (hymns to angels and heroes), and Khurda (lesser rituals and hymns). The Gathas may be as old as the 7th century BC, when Zoroaster is thought to have lived, but most of the Avesta was put together by the Sassanid Persian dynasty, between AD 200 and 640. Zoroastrianism centers on the eternal struggle between a good entity (Ahura Mazda, or Ormuzd) and its evil counterpart (Angra Mainyu, or Ahriman); the religion is still practiced by about 120,000 Parsees in Bombay and a few thousand adherents in Iran and Iraq.