Pericles leads Athenian forces in the expulsion of barbarians from the Thracian peninsula of Gallipoli, in order to establish Athenian colonists in the region. Thus Pericles starts a policy of kleruchos or "out-settlements". This is a form of colonisation where poor and unemployed people are assisted to emigrate to new regions.
A revolt breaks out in Boeotia as the oligarchs of Thebes conspire against the democratic faction in the city. The Athenians, under their general Tolmides, with 1000 hoplites plus other troops from their allies, march into Boeotia to take back the towns revolting against Athenian control. They capture Chaeronea, but are attacked and defeated by the Boeotians at Coronea. As a result, the Athenians are forced to give up control of Boeotia as well as Phocis and Locris, which all fall under the control of hostile oligarchs who quit the Delian League.
The middle component of the Long Walls from Athens to the port city of Piraeus is completed.