The imperialist expansion of Persia pursued by Cyrus the Great, founder of the Achaemenian Empire, already loomed ominously over Egypt by the end of Amasis' rule. The conquest of Egypt was after all a natural objective of that expansionist policy, the Nile Valley being the most important, if not the only source of economic and political power in Africa. When Cambyses, after succeeding his father Cyrus in 529 B.C., had settled his family affairs and the internal problems of his Asiatic empire, he led his army to the eastern borders of Egypt. Amasis, penultimate Pharaoh of Dynasty XXVI, had tried to protect himself against the Persians by an alliance with Polycrates of Samos, but his ally deserted him the moment that an attack by Cambyses became inevitable. There could be little hope of safety for Egypt when Phanes, the general commanding Amasis' troops on the eastern border, chose to betray his king and go over to the more powerful Cambyses, to whom he disclosed all the most valuable Egyptian military secrets. At his advice Cambyses got the support of Bedouins from the Arabian desert whose camels, laden with waterskins, enabled the Persian army to cross the desert and reach Pelusium.

Amasis died probably early in 525 B.C. It therefore fell to his son, Psammetichus III to put up a last stand against the foreign invaders. The Egyptian defence was routed at Pelusium and what was left of the army retreated to Memphis, but before long Memphis fell and Psammetichus was taken prisoner. In accordance with a Persian policy of making defeated sovereigns vassals of the empire, Cambyses treated Psammetichus leniently at first. But soon afterwards he had him killed for inciting rebellion.