After these battles, the Spartan general Brasidas raised an army of allies and helots and marched the length of Greece to the Athenian colony of Amphipolis in Thrace, which controlled several nearby silver mines; their product supplied much of the Athenian war fund. Thucydides was dispatched with a force which arrived too late to stop Brasidas capturing Amphipolis; Thucydides was exiled for this, and, as a result, had the conversations with both sides of the war which inspired him to record its history. Both Brasidas and Cleon were killed in Athenian efforts to retake Amphipolis (see Battle of Amphipolis). The Spartans and Athenians agreed to exchange the hostages for the towns captured by Brasidas, and signed a truce.