The Persians were invading the Greek City-States because Xerxes whose father was Darius wanted revenge on the Greeks for beating the Persians at the battle of marathon. The leader was of course Xerxes. This battle is one of the key events of the Persian wars. Although no one knows for sure Greek historians believe that there was close to 5,000,000 Persians that helped the invasion. An army of around 300 men led by the Spartans went to Thermopylae to fight the Persians. Some believe that they only sent 300 men so that the Athenian people could defeat the Persians at sea. Warriors from other city-states like Thespiae, Thebes and Phocis joined the Spartans in their battle. Plus the Spartans 900 Helots also came. The Greeks were able to hold the pass for at least two days. They fought in a phalanx and killed around 20,000 Persians. Since the pass wasn't very wide only a few Persians could fight at a time. Just when it seemed the Greeks were about to take the win the Persians learned of another way around the pass. The Greeks knew that they were not going to win so they just fought until they all died. After the loss at Thermopylae it gave the Athenians time to retreat to the island of Salamis.
