The Battle of Thermopylae was fought between an alliance of Greek city-states, led by King Leonidas I of Sparta, and the invading Persian Empire, led by King Xerxes I.

It took place during the second Persian invasion of Greece.

A small Greek force of approximately 7,000 men was sent to block the narrow coastal pass of Thermopylae to delay the massive Persian army.

The Greek force was famously led by 300 Spartans.

For two days, the Greeks used the narrow terrain to their advantage, successfully holding off repeated Persian assaults.

The tide turned when a local resident, Ephialtes, betrayed the Greeks by showing the Persians a secret path that allowed them to outflank the Greek position.

Realizing he was surrounded, Leonidas dismissed the bulk of the Greek army and remained to fight a last stand with his 300 Spartans and a few other allies.

Leonidas and his men fought to the death, inflicting heavy casualties on the Persians.

Although a military defeat, the battle became a symbol of Greek courage and sacrifice in the face of overwhelming odds.

The delay gave the Greek city-states, particularly Athens, crucial time to prepare for the subsequent naval battle at Salamis.