In the Gathas, Vishtaspa is repeatedly ("Y. " 46. 14, 51. 16, 53. 2) referred to as a "kavi", which is etymologically a term for a mantic seer, or poet-priest, and in "Yasna" 28. 11 is also used of Zoroaster's enemies. In the Younger Avesta the term is also applied to wise men generally, to include Vishtaspa and his ancestors. In tradition however, the kavis are kings, "evidently because Vīštāspa and his forebears, the 'kavis' "par excellence", were princely rulers. Presumably the gift of prophecy, of mantic poetry, was hereditary in their family. " Both scripture and tradition refer to Vishtaspa's ancestors but do not mention Vishtaspa's successors; Vishtaspa was apparently the last of his line, and the last of the kavis. In Zoroastrian apocalyptic chronology, the dynasties of the world are divided into seven ages, each named after a metal. According to this chronology ("Zand-i Wahman yasn" 2. 16, "Dabistan" 140), Vishtaspa (in Zoroastrian Middle Persian "Wishtasp") ascent to the throne ended the reign of silver, and his reign was over the age of gold. In tradition, the works of Zoroaster were said to have been kept in a royal library that was then destroyed by Alexander the Great. In "Denkard" 3. 420, it is Vishtaspa who is said to have been the king who had those texts made and placed in the royal library.