 He is not mentioned in the histories of Herodotus or Ctesias, and many scholars doubt that he actually existed.The question of his existence impacts on whether the kingdom of the Medes merged peacefully with that of the Persians in about 537 BC, as narrated by Xenophon (8.6.22, 8.7.1), or was subjugated in the rebellion of the Persians against Cyrus' grandfather in 559 BC, a date derived from Herodotus (1.214) and almost universally accepted by current scholarship.According to Xenophon's "Cyropaedia" (1.5.2), Cyaxares II followed king Astyages to the throne of the Median Empire, and he was also the brother of Mandane, Cyrus the Great's mother (1.2.1, 1.4.7).