It was in the sixth year of Nabonidus (549 BC) that Cyrus the Great, the Achaemenid Persian king of Anshan in Elam, revolted against his suzerain Astyages, king of the Manda or Medes, at Ecbatana. Astyages' army betrayed him to his enemy, and Cyrus established himself at Ecbatana, thus putting an end to the empire of the Medes and making the Persian faction dominant among the Iranic peoples. Three years later Cyrus had become king of all Persia, and was engaged in a campaign to put down a revolt among the Assyrians. Meanwhile, Nabonidus had established a camp in the desert of his colony of Arabia, near the southern frontier of his kingdom, leaving his son Belshazzar (Belsharutsur) in command of the army.