The Persian Conquest of Egypt of 525 BC saw Cambyses II of Persia conquer the fourth major power of the ancient near east, completing the series of conquests begun by his father Cyrus II the Great.
Cambyses II inherited the throne after his father's death in battle in the north-eastern corner of his empire in 530 BC. Cambyses quickly secured the throne, although only after killing his brother Bardiya.
It must have been clear that the Persians would soon move against Egypt. Pharaoh Ahmose II of the 26th Dynasty, who had based his rule on a renewed sense of Egyptian nationalism, hired Greek mercenaries to prepare for the upcoming invasion, but he died before the fighting began. Ahmose was succeeded by his son Psamtik III, but his reign would be very short-lived.
Herodotus records a series of possible reasons for the invasion, all of them largely personal. The first, and the one he supports and says that the Persians gave in his time, is that an Egyptian doctor who had been sent to Persian convinced Cambyses to ask for Ahmose's daughter's hand in marriage. Ahmose didn't want to sent his daughter to become a concubine at the Persian court, and so decided to send Nitetis, daughter of Apries, the previous pharaoh in her place. At first Nitetis played along with the plot, but she eventually revealed her true identity. Cambyses was furious and decided to attack
Herodotus also records an Egyptian version of the story. In this version it was Cyrus who requested the Egyptian princess, and Cambyses was their son, giving him a legitimate claim to the Egyptian throne. Unfortunately for this story, Cambyses's mother is known to have been Cassandane, daughter of Pharnaspes. This was said to have been the story told in Egypt, and was probably developed in an attempt to avoid the shame of having been conquered.
Finally Herodotus records a story which he dismissed as unbelievable. In this version Nitetis has been sent to the court of Cyrus, where she has won the emperors favour and overshadowed Cassandane. Cambyses, aged only ten, decided to invade Egypt to take revenge for the insult to his mother.
While it is possible that there might have been some truth in these stories, there is no real need to hunt for a motive. Cyrus had been a great conqueror. Cambyses would have wanted to prove himself to be his father's equal, and Egypt was the obvious target for an invasion. An independent Egypt also posed a threat to Persian control of Palestine and Syria, as would be demonstrated later in the life of the Persian Empire (and again during the long series of wars between Ptolemaic Egypt and the Seleucid Empire).
Cambyses had help from several directions. He was sent 40 triremes by Polycrates, tyrant of Samos. Phanos, one of the Greek mercenary generals, betrayed Psamtik and sent important information to Cambyses. Finally the Arabs provided him with water during the difficult crossing of the Sinai Desert in 525.
Cambyses defeated the Egyptians in battle at Pelusium in the Nile Delta and they retreated to Memphis. The Persians captured Helopolis and then besieged Memphis. The city soon fell and Psamtik was captured. The deposed Pharoah was taken into captivity at Susa and Cambyses set about establishing his rule in Egypt.
After the relatively easy conquest of Egypt, Cambyses is said to have attempted three further conquests, all of which failed. An attempt to attack Carthage failed after his Phoenician sailors refused to attack their former colony. An army sent to the Oasis of Amon in the desert west of the Nile was said to have been destroyed by a sand storm. Finally Cambyses led an army south into Nubia, achieving some successes but suffering from a lack of supplies.
In the aftermath of these campaigns Cambyses set up garrisons at Daphnae in the eastern part of the Nile delta, Memphis and Elephantine. This effort took several years, and Cambyses was still away from home in 522 BC when a revolt broke out in Iran. The rebels were led by someone claiming to be Cambyses's brother Bardiya. Cambyses rushed home, but died during the journey. This ended the rule of the direct line of Cyrus, and Cambyses was succeeded by Darius I, a more distant member of the family.
Egypt would prove to be one of the more troublesome provinces of the Empire. Cambyses himself appears to have been fairly popular in the country, and was accepted as the legitimate Pharaoh of a new dynasty. After his death Egypt revolted successfully in 486, but was re-conquered in the following year. A second revolt, in 459, lasted until 454. A third revolt, in 405, was more successful. By this point the Persian Empire was past its peak, and the Egyptians were able to fight off several attempts at conquest, remaining independent until 343. A final revolt was crushed in 337-336, but only a few years later Alexander the Great overthrew Darius III, the last Achaemenid emperor, marking the start of a new period in Egyptian history.