The naval Battle of Pylos takes place in 425 BCE during the Peloponnesian War at the peninsula of Pylos, on the present-day Bay of Navarino in Messenia, and is 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 had fortified the peninsula, and a small force had been left there when the fleet departed again.

The establishment of an Athenian garrison in Spartan territory frightens the Spartan leadership, and the Spartan army, which has been ravaging Attica under the command of Agis, ends their expedition (the expedition only lasted fifteen days) and marches home, and the Spartan fleet at Corcyra sails to Pylos.Demosthenes has five triremes and their complements of soldiers as a garrison, and is reinforced by forty hoplites from a Messenian ship that had happened to stop at Pylos.

In total, Demosthenes probably had about six hundred men, only ninety of whom are hoplites.

He sends two of his triremes to intercept the Athenian fleet and inform Sophocles and Eurymedon of his danger.

The Spartans, meanwhile, have forty-three triremes and a large land army.

Finding himself thus outnumbered, Demosthenes pulls his remaining three triremes up on land and arms their crews with whatever weapons are at hand.

He places the largest part of his force at the strongly fortified point facing the land.

Demosthenes then hand-picks sixty hoplites and a few archers and brings them to the point where he anticipates the Spartans will launch their amphibious assault.

Demosthenes expects that the Spartans will hit the southwest corner of the peninsula where the defensive wall is the weakest and the land is most suitable for a landing.

The Spartans attacked where Demosthenes had expected, and the Athenians are faced with simultaneous assaults from land and sea.

The Athenians hold off the Spartans for a day and a half, however, causing the Spartans to cease their attempts to storm Pylos and instead settle in for a siege.While the Spartans' siege preparations are underway, the Athenian fleet,fifty triremes strong, arrives from Zacynthus.

The Spartans fail to blockade the entrance of the harbor, so the Athenians are able to sail in and catch the Spartans unprepared; the Spartan fleet is decisively defeated, and the Athenians gain control of the harbor.

In doing so, they trap four hundred and twenty Spartan hoplites on the island of Sphacteria, off of Pylos.

One hundred and twenty of these are from the Spartiate class, and their peril throws the Spartan government into a panic.

Members of the government are dispatched to the scene, and negotiate an armistice on the spot; the entire Spartan fleet is surrendered to the Athenians as a guarantee for Spartan good conduct, and ambassadors are sent to Athens to seek a permanent peace.

When these negotiations fail, the Athenians retain possession of the Spartan ships on a pretext, and settle in to besiege the hoplites on Sphacteria; eventually, in the Battle of Sphacteria, those hoplites are captured and taken as hostages to Athens.

Pylos remains in Athenian hands, and is used as a base for raids into Spartan territory and as a refuge for fleeing Spartan Helots.