Changes

The final and perhaps most important step the Sasanians took in the evolution of Zoroastrianism was to finally put the oral verses of the Avesta into writing. This process took place during the fifth or sixth centuries and totaled twenty-one books, including the following: gathas (songs), yashts (hymns to Mithra and other lesser gods), and the Vendidad (laws). Copies of the original Avesta, which were compiled in the Avestan language, were all destroyed in the Arab, Mongol, and Turkish invasions of Persia in the Middle Ages, but the Middle Persian, or Pahlavi, Zand of the Sasanians survived. <ref> Boyce 1990, pgs. 1-4</ref> Since the only extant version of the Avesta is the Zand of the Sasanians, it is often called the Zand or Zend-Avesta.

[[File: Zoroastrian_temple_in_Mazra_Kalantar.jpg|300px|thumbnail|left|A Modern Zoroastrian Temple in Iran]]