“So Darius son of Hystaspes was made king, and the whole of Asia, which Cyrus first and Cambyses after him had conquered, was subject to him…and everything was full of his power. First he made and set up a carved stone, upon which was cut the figure of a horseman, with this inscription: ‘Darius son of Hystaspes, aided by the excellence of his horse, and of Oebares his groom, got possession of the kingdom of Persia.'” – Herodotus

Cambyses successfully conquered Egypt, but forays beyond its frontiers met with frustration and disaster.  The promise of Lydian gold lured Polycrates to a gruesome death in Sardis.  Bardiya briefly wrestled the Persian Empire from his brother, only to lose it to a conspiracy of nobles led by Darius.