The Battle of Thermopylae was fought between an alliance of Greek city-states, led by King Leonidas I of Sparta, and the Persian Empire of Xerxes I. A small Greek force, famously including 300 Spartans, held the narrow pass of Thermopylae for three days against a massive Persian army of over 100,000 men. Although the Greeks were eventually betrayed and defeated when a local named Ephialtes showed the Persians a mountain path, the stand allowed the rest of the Greek fleet and army to retreat and prepare. The sacrifice of Leonidas and his men became a symbol of heroic resistance against overwhelming odds and the defense of freedom. It set the stage for later Greek victories at Salamis and Plataea, which ended the Persian invasion. Today, it remains one of history's most famous examples of bravery and military tactics using terrain to negate numerical advantages.