Cambyses II was the eldest son of Cyrus II, the founder of the Achaemenid (or Persian) Empire, whose father was Cambyses I.
The exact date of his birth is not known but is estimated to be around 560 b.c.e., and he was said by the Greek writer Herodotus of Halicarnassus to be the eldest son of Cassandane, daughter of Pharnaspes, also a member of the Achaemenid ruling family.
Cyrus took control of Babylonia in 539 b.c.e. and returned to Ecbatana, one of the royal capitals, leaving his son Cambyses as his representative. Cambyses made his headquarters at Sippar, a town to the north of the city of Babylon.
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However, following his father’s policy, he was active in taking part in the spring New Year ceremonies that took place in Babylon. For eight years, on behalf of his father, Cambyses took charge of the area of Babylonia, and the evidence we have suggests a prince hard at work in his routine duties.
In 530 b.c.e. his father, Cyrus, set off to solve problems on the northeastern border of his empire and, following Persian custom, appointed Cambyses his regent, at the same time giving him permission to be called king of Babylon.
News of his father’s death in action reached Cambyses in Babylonia in September 530 b.c.e., and he assumed the full title King of Babylon, King of Lands, and by local custom married his two sisters, Atossa and Roxana.
The most significant event of Cambyses’ reign was his invasion of Egypt, which began a few years after his accession. Most likely before he left Persia for the invasion Cambyses had his brother, variously called Bardiya or Smerdis, quietly killed as a precaution against his leading a rebellion in the king’s absence.
Cambyses crossed the Sinai desert, Egypt’s first line of defense, and met the Egyptian army under the command of Psamtik III, at Pelusium. The battle went the Persian way not least because of the treachery of Polycrates of Samos, whose navy Psamtik erroneously thought he had secured but who on the day of combat fought for Cambyses.
Heliopolis (the site of modern-day Cairo) was soon thereafter taken by siege, Psamtik fled across the river to Memphis, which early in 525 b.c.e. was also taken, and Cambyses was proclaimed the new pharaoh.
A year later Cambyses marched south down the Nile and occupied Thebes. From there he considered invading Ethiopia but decided to stop at the border, Ethiopia becoming a vassal state. There is much debate as to how Cambyses behaved toward the religion of the Egyptians.
Herodotus claims that he committed various atrocities and that this was due to Cambyses’ being mad. However, not everyone agrees with Herodotus, and it is very possible that what Herodotus records is propaganda against Cambyses after Darius I’s accession in 522 b.c.e.
In the spring of 522 b.c.e. a man called Gaumata, claiming to be Cambyses’ brother Bardiya, seized the Achaemenid throne. Cambyses began the journey back to Persia to deal with the usurper but died early on in the journey. Whether his death was from suicide or from accidental poisoning following a sword wound is still debated.