Cambyses II, Persia’s second Achaemenid king, either commits suicide or dies accidentally in Syria in the summer of 522 BCE while returning to Persia from Egypt, supposedly to deal with a revolt by a usurper claiming to be Cambyses’ younger brother Bardiya, called Smerdis by the Greeks. (The Greek historian Herodotus, writing a century later, will allege in his history that Cambyses was insane.)

Having supposedly taken the throne in March, Bardiya reigns for no more than eight months before being slain in September by Darius—a member of the late Cambyses’ royal bodyguard—and other Persian nobles suspicious of his origin.

Darius, the son of Hystaspes, the satrap of Parthia, ascends the Achaemenid throne, claiming that he is restoring the kingship to the rightful Achaemenid royal family, of which his is a collateral branch. (As Darius’ father and grandfather are alive at his accession, it is unlikely that he is next in line to the throne. According to Darius' account in his later trilingual inscription at Bisitun, Cambyses had secretly murdered Bardiya years before, and the usurping Bardiya was a successful impersonation by Gaumata the Magian. Certain modern scholars consider that Darius fabricated the story of Gaumata to justify his actions and that his murdered predecessor had indeed been a son of Cyrus.)

Cambyses’s conquest of Egypt has allowed the relatively benevolent Darius to rule a centralized empire from the Mediterranean to the Indus.

He divides the Achaemenid empire into satrapies for administrative convenience, organizes the postal system on the royal roads, institutes an efficient central bureaucracy, and strives to standardize legal practices throughout the empire with the imposition of Universal Law (the King’s Law).

He mints gold coins called “darics.”

Zoroastrianism spreads with Darius’s encouragement.