The Athenians and Egyptians thus settled down to besiege the White Castle. The siege evidently did not progress well, and probably lasted for at least four years, since Thucydides says that their whole expedition lasted 6 years,and of this time the final 18 months was occupied with the Siege of Prosoptis.

According to Thucydides, at first Artaxerxes sent Megabazus to try and bribe the Spartans into invading Attica, to draw off the Athenian forces from Egypt. When this failed, he instead assembled a large army under (confusingly) Megabyzus, and dispatched it to Egypt. Diodorus has more or less the same story, with more detail; after the attempt at bribery failed, Artaxerxes put Megabyzus and Artabazus in charge of 300,000 men, with instructions to quell the revolt. They went first from Persia to Cilicia and gathered a fleet of 300 triremes from the Cilicians, Phoenicians and Cypriots, and spent a year training their men. Then they finally headed to Egypt. Modern estimates, however, place the number of Persian troops at the considerably lower figure of 25,000 men given that it would have been highly impractical to deprive the already strained satrapies of any more man power than that. Thucydides does not mention Artabazus, who is reported by Herodotus to have taken part in the Second Persian invasion of Greece; Diodorus may be mistaken about his presence in this campaign. It is clearly possible that the Persian forces did spend some prolonged time in training, since it took four years for them to respond to the Egyptian victory at Papremis. Although neither author gives many details, it is clear that when Megabyzus finally arrived in Egypt, he was able to quickly lift the siege of Memphis, defeating the Egyptians in battle, and driving the Athenians from Memphis.