By 546 BCE, Cyrus the Great had defeated Croesus, the Lydian king of fabled wealth, and had secured control of the Aegean coast of Asia Minor, Armenia, and the Greek colonies along the Levant. Moving east, he took Parthia (land of the Arsacids, not to be confused with Parsa, which was to the southwest), Chorasmis, and Bactria. He besieged and captured Babylon in 539 and released the Jews who had been held captive there, thus earning his immortalization in the Book of Isaiah. When he died in 529, Cyrus's kingdom extended as far east as the Hindu Kush in present-day Afghanistan.
His successors were less successful. Cyrus's unstable son, Cambyses II, conquered Egypt but later he died in July, 522 BCE, as the result of either an accident or suicide during a revolt led by a priest, Gaumata, who usurped the throne by pretending to be Bardiya (Cambyses' brother, who had been assassinated secretly before Cambyses started out for his Egyptian campaign in 525 BCE) until overthrown in 522 BCE by a member of a lateral branch of the Achaemenid family, Darius I (also known as Darayarahush or Darius the Great). Darius attacked the Greek mainland, which had supported rebellious Greek colonies under his aegis, but as a result of his defeat at the Battle of Marathon in 490 was forced to retract the limits of the empire to Asia Minor.