Spartan troops occupied Sphacteria during the Battle of Pylos in 425 BCE.
Sphacteria is a long, narrow island in the Ionian Sea, lying just off the southwestern Peloponnese near the harbor of Pylos. During the Peloponnesian War, a Spartan force landed there to strengthen the area and guard the entrance to the harbor.
Athenians later captured the harbor and blockaded the Spartan soldiers on Sphacteria. After fighting and an extended siege, 292 Spartan hoplites surrendered in 425 BCE, including 120 full Spartan citizens. Their capture shocked the Greek world because Spartans were renowned for refusing to surrender.
The episode became an important Athenian success early in the war and helped persuade Sparta to seek negotiations. Sphacteria is sometimes confused with Pylos: Pylos was the mainland harbor and fortified position, while Sphacteria was the offshore island where the trapped Spartan troops fought.