'War with the Persians continued, however. In 460 BC, Egypt had revolted under Inarus and Amyrtaeus, who requested aid from Athens. Pericles led 250 ships, originally intended to attack Cyprus, to their aid because it would hurt Persia. Persia's image had already been hurt when it failed to conquer the Greeks and Pericles wanted to further this. After four years, however, the rebellion was defeated by general Megabyzus, who captured the greater part of the Athenian forces. In fact, according to Isocrates, the Athenians and their allies lost some 20,000 men in the expedition. The remainder escaped to Cyrene and thence returned home.
This was Athenians' main (public) reason for moving the treasury of the League from Delos to Athens, further consolidating their control over the League. The Persians followed up their victory by sending a fleet to re-establish their control over Cyprus, and 200 ships were sent out to counter them under Cimon, who returned from ostracism in 451 BC. He died during the blockade of Citium, though the fleet won a double victory by land and sea over the Persians off Salamis.
This battle was the last major one fought against the Persians. Many writers report that a formal peace treaty, known as the Peace of Callias, was formalized in 450 BC, but some writers believe that the treaty was a myth created later to inflate the stature of Athens. However, an understanding was definitely reached, enabling the Athenians to focus their attention on events in Greece proper.'