How did the Spartans and the Athenians defeat the Persians?

The second stage of the war saw the Persians arrive on the Greek shore with perhaps as many as 2,000,000 men, between their army and navy, under the command of king Xeres I (519-465 B. C.), son of the deceased Darius I. An advance party of only 5,000 Greeks, including Spartans, Phocians and Locrians, under the command of one of the Spartan kings, Leonidas (a descendent of Hercules), held off the advancing Persian forces at the narrow pass between the cliffs and the sea at Thermopylae (the famous "Pass of Thermopylae").