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. The Yasht's allusions to conflicts are amplified in the 9th–11th century books of Zoroastrian tradition, where the conflicts are portrayed as outright battles of the faith. So for example the surviving fragments of a fragmentary text that celebrates the deeds of Zairivairi, Vishtaspa's brother and captain of his forces against Arejat.aspa, chief of the Hyonas. According to that text (Ayadgar i Zareran, 10–11), upon hearing of Vishtaspa's conversion, Arejat.aspa sent messengers to demand that Vishtaspa "abandon 'the pure Mazda-worshipping religion which he had received from Ohrmazd', and should become once more 'of the same religion'" as himself. The battle that following Vishtaspa's refusal left Vishtaspa victorious. The conversion of Vishtaspa is likewise a theme of the 9th–11th century books, and these legends remain the "best known and most current" among Zoroastrians today. According to this tradition, when Zoroaster arrived at Vishtaspa's court, the prophet was "met with hostility from the kayags and karabs (kavis and karapans), with whom he disputed at a great assembly–a tradition which may well be based on reality, for [Vishtaspa] must have had his own priests and seers, who would hardly have welcomed a new prophet claiming divine authority. "