The Avesta is a collection of the central religious texts of Zoroastrianism written in the old Iranian dialect of Avestan. The history of the Avesta is speculated upon in many Pahlavi texts with varying degrees of authority, with the current version of the Avesta dating at oldest from the times of the Sasanian Empire. According to Middle Persian tradition, Ahura Mazda created the twenty-one Nasks of the original Avesta which Zoroaster brought to Vishtaspa. Here, two copies were created, one which was put in the house of archives and the other put in the Imperial treasury. During Alexander's conquest of Persia, the Avesta (written on 1200 ox-hides) was burned, and the scientific sections that the Greeks could use were dispersed among themselves. However, there is no strong evidence historically towards these claims and they remain contested despite affirmations from the Zoroastrian tradition, whether it be the "Denkart", "Tansar-nāma, Ardāy Wirāz Nāmag, Bundahsin, Zand i Wahman Yasn  "or the transmitted oral tradition.