Leonidas

Becomes king after his half-brother Cleomenes I dies. Sparta is one of two dominant Greek powers. The Persians under Darius have already invaded once, at Marathon, and been repelled by Athens. Everyone knows they'll come back.

Marches to Thermopylae with 300 Spartan soldiers and roughly 7,000 allied Greeks to block Xerxes and an army numbering between 100,000 and 300,000. The pass is narrow. The plan is to hold it like a cork in a bottle.

A local named Ephialtes betrays the Greeks by showing the Persians a mountain path around the pass. Leonidas dismisses most of the allied army. He keeps his 300 Spartans, 700 Thespians, and 400 Thebans for a last stand.

Killed on the third day of fighting. The Persians overwhelm the rearguard from both sides. Herodotus says the Greeks fight with swords, then hands and teeth. Xerxes orders Leonidas beheaded and crucified. The Greeks hold long enough for the fleet to regroup at Salamis.

Forty Greek states unite after Thermopylae. At the Battle of Plataea the next summer, the combined Greek army destroys the Persian land forces. Sparta leads the charge. The inscription at Thermopylae reads: 'Go tell the Spartans, stranger passing by, that here obedient to their laws we lie.'