Xerxes the Great was determined to punish the Greeks for their victory over Persia at Marathon. After several years of planning, Xerxes’ huge army and navy travelled south from Sardis, through Thrace and Macedonia. While the land army was advancing, there were several severe storms that shipwrecked much of the Persian fleet. After crossing the Hellespont (the Dardanelles), Xerxes reached the narrow pass of Thermopylae. The Spartan Greeks were guarding a gap in the cliff wall, making it difficult for Xerxes’ troops to progress. After seven days, Xerxes’ 10,000 elite ‘Immortals’ massacred King Leonidas’ Spartan army. Xerxes advanced southwards, capturing Boetia and Attica. He then entered and burned Athens. The Greek forces escaped to Salamis, where their navy destroyed the depleted Persian fleet. Xerxes left Greece, leaving General Mardonius to fight on. The Persians were defeated the following year (479 BCE) and were eventually driven out of Greece, the Aegean and Ionian islands.