(from the article `Avestan language`) eastern Iranian language of the Avesta, the sacred book of Zoroastrianism. Avestan falls into two strata, the older being that of the Gths, which ... ...period ( 224–651) genuinely reflected the teachings of Zoroaster. A third question is the extent to which the sourcesthe Avesta (the Zor... Found on http://www.britannica.com/eb/a-z/g/13