The Grecian fleet, under the command of the Spartan Eurybiades, took up its station off that portion of the northern coast of Euboea which faces Magnesia and the entrance to the Thessalian gulf and which was called Artemisium, from a neighbouring temple of Artemis (Diana). It was, however, only a small land-force that was sent to the defence of Thermopylae. When the arrival of Xerxes at Therma became known, the Greeks were upon the point of celebrating the Olympic games, and the festival of the Carnean Apollo, which was observed with great solemnity at Sparta and in other Doric states. The Peloponnesians therefore sent forward only 300 Spartans and 3000 hoplites from other Peloponnesian states, under the command of the Spartan king Leonidas, a force which they thought would be sufficient to maintain the pass till the festivals were over. In his march northwards Leonidas received additions from the Thespians, Phocians, and Locrians, so that he had under his command at Thermopylae about 7000 men.
Meanwhile Xerxes had arrived within sight of Thermopylae. He had heard that a handful of desperate men, commanded by a Spartan, had determined to dispute his passage, but he refused to believe the news. He was still more astonished when a horseman, whom he had sent to reconnoitre, brought back word that he had seen several Spartans outside the wall in front of the pass, some amusing themselves with gymnastic exercises, and others combing their long hair. In great perplexity, he sent for the exiled Spartan king Demaratus, who had accompanied him from Persia, and asked him the meaning of such madness. Demaratus replied, that the Spartans would defend the pass to the death, and that it was their practice to dress their heads with peculiar care when they were going to battle. Later writers relate that Xerxes sent to them to deliver up their arms. Leonidas desired him "to come and take them." One of the Spartans being told that "the Persian host was so prodigious that their arrows would conceal the sun:" --"So much the better" (he replied), "we shall then fight in the shade."