Sparta led the allied Greek city-states at the Battle of Thermopylae.
The battle took place in 480 BC during Xerxes I’s invasion of Greece. Sparta supplied the commander, King Leonidas I, and held the leading military position in the land defence, while other Greek states contributed troops. The allied force chose Thermopylae because its narrow pass could limit the Persian army’s numerical advantage.
The famous Spartan contingent numbered about 300 citizens, but the defenders were not exclusively Spartan. Thousands of other Greeks, including Thespians, Thebans, Phocians, Locrians, and Peloponnesian troops, also fought there. After a local named Ephialtes revealed a mountain path, the Persians outflanked the main force. Leonidas remained with a rearguard that included Spartans and other Greek soldiers.
A common misconception is that Sparta alone defended the pass. Sparta provided the famous king and elite contingent, but Thermopylae was an allied operation. Athens played a major role elsewhere in the same defensive strategy, especially at sea, where its fleet helped confront Persia at Artemisium and later Salamis.