The island of Naxos wishes to secede from the Delian League, but is blockaded by Athens and forced to surrender. Naxos becomes a tribute-paying member of the Delian League. This action is considered high-handed and resented by the other Greek city states.
Thasos revolts from the Delian League. The revolt arises from rivalry over trade with the Thracian hinterland and, in particular, over the ownership of a gold mine. Athens under Kimon lays siege to Thasos after the Athenian fleet defeats the Thasos fleet.
When the Messenian helots (serfs) revolt against their Spartan masters following the severe earthquake, King Archidamus II organises the defence of Sparta. The helots fortify themselves at Mount Ithome.
In Athens, the democratic statesman Ephialtes and the young Pericles attempt to get the oligarchic Kimonostracized for allegedly receiving bribes. Kimon is charged by Pericles and other democratic politicians with having been bribed not to attack the King of Macedonia (who may have been suspected of covertly helping the Thasian rebels). Though Kimon is acquitted, his influence on the Athenian people is waning.
Kimon seeks the support of Athens' citizens to providing help to Sparta. Although Ephialtes maintains that Sparta is Athens' rival for power and should be left to fend for itself, Kimon's view prevails. Kimon then leads 4,000 hoplites to Mount Ithome.
After an attempt to storm Mt. Ithome fails, the Spartans start to distrust the Athenians over concerns that they may take the side of the helots. Retaining their other allies, the Spartans sent Kimon and his men home. This insulting rebuff causes the collapse of Kimon's popularity at Athens. Outrage over the dismissal swings Athenian opinion towards Ephialtes' views.
Ephialtes passes a law in the Athenian ecclesia, which reforms the Areopagus, limiting its power to judging cases of homicide and religious crimes. He considers the Areopagus to be the centre of conservatism and Ephialtes' victory is seen as a defeat for the conservatives and the members of the oligarchy.
Argos, taking advantage of Spartan preoccupation with the revolt of its helots, finally conquers Mycenae. The inhabitants of the town are dispersed, with some finding their way into Macedonia.
Ephialtes, with the support of Pericles, reduces the power of the Athenian Council of Areopagus (filled with ex-archons and so a stronghold of oligarchy) and transfers them to the people, i.e. the Council of Five Hundred, the Assembly and the popular law courts. The office of Judge is made a paid position and is recruited by lot from a list to which every citizen can have his name added.
Egypt revolts against Persian rule. The Egyptian leader, Inaros, asks Athens for assistance, which is willingly provided as Athens has plans to trade with and colonise Egypt. A force of 200 Athenian triremes, which is campaigning in Cyprus, is immediately ordered to Egypt to render assistance.
Achaemenes, Persian satrap (governor) of Egypt, is defeated and slain in a battle at Papremis, on the banks of the Nile River, by Egyptian forces.
Ducetius, a Hellenised leader of the Siculi, an ancient people of Sicily, takes advantage of the confusion that follows the collapse of the tyranny in Syracuse and other Sicilian states. With the support of the Syracusan democracy, he drives out the colonists of the former tyrant Hieron from Catana and restores it to its original inhabitants.
The sculpture Apollo with battling Lapiths and centaurs is built on the west pediment of the Temple of Zeus in Olympia (approximate date). Only fragments remain and are today preserved at the Archaeological museum in Olympia.
A metope relief of Athena, Heracles and Atlas are made on a frieze in the Temple of Zeus in Olympia (approximate date). It is now preserved at the Archaeological museum in Olympia.