The Battle of Thermopylae was part of the Second Persian War. Wanting to avenge the Battle of Marathon loss, Xerxes of Persia sent an army to fight 300 Spartans, Helots, and northern city-state soldiers, defeating them after three days. The Spartan army was led by King Leonidas. The Spartans were victorious for the first 2 days of battle despite being outnumbered by the Persians. The Spartans lost after a betrayal by one of their own who revealed a secret path behind the Greek lines.
