The battle of Thermopylae was fought between an alliance of Greek cities, led by king Leonidas of Sparta, and the Persian empire of Xerxes. During the second Persian invasion of Greece, it took place simultaneously with the naval battle of Artemisium, at the narrow coastal pass of Thermopylae. The Persian invasion was a delayed response to the defeat of the first Persian invasion of Greece, which had been ended by the Athenian victory at the Battle of Marathon. Xerxes had assembled a huge army and navy, and set out to conquer all of Greece. The Athenian politician and general Themistocles had proposed that the allied Greeks block the advance of the Persian army at the pass of Thermopylae, and simultaneously block the Persian navy at the Straits of Artemisium.
