group of Spartan soldiers on Sphacteria as he waited for them to surrender. But weeks later he proved unable to finish them off. Instead, the inexperienced Cleon boasted in the Assembly that he could end the affair, and did win a great victory at the Battle of Sphacteria. In a shocking turn of events, 300 Spartan hoplites encircled by Athenian forces surrendered. The Spartan image of invincibility took significant damage. The Athenians jailed Sphacterian hostages in Athens and resolved to execute the captured Spartans if a Peloponnesian army invades Attica again. 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. Amphipolis controlled several nearby silver mines whose that supplied much of the Athenian war fund. A force led by Thucydides was dispatched but arrived too late to stop Brasidas capturing Amphipolis; Thucydides was exiled for this, and, as a result, had 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. Peace of Nicias (421 BC) With the death of Cleon and Brasidas, both zealous war hawks for their nations, the Peace of Nicias was able to last six years. However, it was a time of constant skirmishes in and around the Peloponnese. While the Spartans refrained from action themselves, some of their allies began to talk of revolt. They were supported in this by Argos, a powerful Peloponnesian state that had remained independent of Lacedaemon. With the support of the Athenians, the Argives forged a coalition of democratic states in the Peloponnese, including the powerful states of Mantinea and Elis. Early Spartan attempts to break up the coalition failed, and the leadership of the Spartan king Agis was called into question. Emboldened, the Argives and their allies, with the support of a small Athenian force under Alcibiades, moved to seize the city of Tegea, near Sparta. The Battle of Mantinea was the largest land battle within Greece during the Peloponnesian War. The Lacedaemonians, with their neighbors the Tegeans, faced the combined armies of Argos, Athens, Mantinea, and Arcadia. In the battle, the allied coalition scored early successes, but failed to capitalize