The naval Battle of Pylos took place in 425 BC during the Peloponnesian War at the peninsula of Pylos, on the present-day Bay of Navarino in Messenia, and was an Athenian victory over Sparta. An Athenian fleet had been driven ashore at Pylos by a storm, and, at the instigation of Demosthenes, the Athenian soldiers fortified the peninsula, and a small force was left there when the fleet departed again. The establishment of an Athenian garrison in Spartan territory frightened the Spartan leadership, and the Spartan army, which had been ravaging Attica under the command of Agis, ended their expedition and marched home, while the Spartan fleet at Corcyra sailed to Pylos.

The Peloponnesian War was an ancient Greek war fought between Athens and Sparta and their respective allies for the hegemony of the Greek world. The war remained undecided for a long time, until the decisive intervention of the Persian Empire in support of Sparta. Led by Lysander, the Spartan fleet, built with Persian subsidies, finally defeated Athens and started a period of Spartan hegemony over Greece.