On the death of Cyrus the Great the Achaemenid Empire passed to his son, Cambyses II (529–522 BCE). There may have been some degree of unrest throughout the empire at the time of Cyrus' death, for Cambyses apparently felt it necessary secretly to kill his brother, Bardiya (Smerdis), in order to protect his rear while leading the campaign against Egypt in 525 BCE. The pharaoh Ahmose II of the 26th dynasty sought to shore up his defenses by hiring Greek mercenaries, but was betrayed by the Greeks. Cambyses successfully managed the crossing of the hostile Sinai Desert, traditionally Egypt's first and strongest line of defense, and brought the Egyptians under Psamtik III, son and successor of Ahmose, to battle at Pelusium. The Egyptians lost and retired to Memphis; the city fell to the Persians and the Pharaoh was carried off in captivity to Susa. Three subsidiary campaigns were then mounted, all of which are reported as failures: one against Carthage, but the Phoenician sailors, who were the backbone of the Persian navy, declined to sail against their own colony; one against the oasis of Amon (in the Egyptian desert west of the Nile), which, according to Herodotus, was defeated by a massive sandstorm; and one led by Cambyses himself to Nubia. This latter effort was partly successful, but the army suffered badly from a lack of proper provisions on the return march. Egypt was then garrisoned at three major points: Daphnae in the east delta, Memphis, and Elephantine, where Jewish mercenaries formed the main body of troops.
In 522 BCE news reached Cambyses of a revolt in Iran led by an impostor claiming to be Bardiya, Cambyses' brother. Several provinces of the empire accepted the new ruler, who bribed his subjects with a remission of taxes for three years. Hastening home to regain control, Cambyses died—possibly by his own hand, more probably from infection following an accidental sword wound. Darius, a leading general in Cambyses'army and one of the princes of the Achaemenid family, raced homeward with the troopsin order to crush the rebellion in a manner profitable to himself.
Cambyses has been rather mistreated in the sources, thanks partly to the prejudices of Herodotus' Egyptian informers and partly to the propaganda motives of Darius I. Cambyses is reported to have ruled the Egyptians harshly and to have desecrated the irreligious ceremonies and shrines. His military campaigns out of Egypt were all reported as failures. He was accused of suicide in the face of revolt at home. It was even suggested that he was mad. There is, however, little solid contemporary evidence to support these charges.