 However, his son Cambyses was the heir to the throne, not Darius, causing Cyrus to wonder if Darius was forming treasonable and ambitious designs.This led Cyrus to order Hystaspes to go back to Persis and watch over his son strictly, until Cyrus himself returned.Darius did not seem to have any treasonous thoughts as Cambyses II ascended the throne peacefully; and, through promotion, Darius was eventually elevated to be Cambyses's personal lancer.