In the Sasanians' legendary genealogy that has appeared in Kar-Namag i Ardashir i Pabagan, the relation between the Sasanians and the Achaemenids is mentioned. In the book, the thought that has been reflected is the relation of Sasan, the ancestor of the Sasanian house, with Darius's descendants on one hand and the local Persian kings on the other hand; though in the fifth century, the Sasanians attributed their lineage to the mythical kings of Avesta or Kayanians; and its proof is the addition of the prefix "Kay" to the aliases of the Sasanian shahanshahs.