With the Greeks making ready at Thermopylae and Artemisium, Xerxes fleet set sail out of Therma eleven days after the army had left it. The Persian fleet made it to Sepias and the army to Thermopylae without any significant loss. The fleet had "1207 ships belonging to the various nations that had set sail from Asia, with its original compliment of 241,400 men-allowing 200 each ship..in addition to the crew, thirty fighting men..making an additional 36,210(VII, 184)." Following the battle ships were 3000 pentecomers adding another 240,000 men to the fleet making the "total number of men aboard..517,610 (VII, 184)." Xerxes army was no less of a force including the infantry that was "1,700,000 strong and the cavalry 80,000. Then there was the Arabian camel corps and the Libyan Charioteers..as a further 20,000 (VII, 184). The total then for Xerxes force excluding servants and men for transport was 2,317,610. Further he gathered troops along his march through Europe so that at Thermopylae the force was 2,641,610 strong. Including all servants, male followers, and boat crews "Xerxes, the son of Darius, reached Sepias and Thermopylae at the head of an army consisting, in all, of 5,283,220 men (VII, 186)." After reaching Sepias the Persian fleet came upon a 'Hellespontian' storm and "four hundred ships are said to have been lost in this disaster, and the loss of life and of treasure beyond reckoning (VII, 190)." After the storm and the mass destruction of the fleet the Greeks sacrificed to Poseidon in thanks for his help in the war.
Xerxes army stopped at Trachis in the Malian territory, while the Greeks held the pass at Thermopylae. One army had the south and the other the north. The Greek force that was waiting for the Persians included Spartans, Corinthians, and various other soldiers from all over the Peloponnese. They told everyone that there were more support troops on the way and the sea was firmly held by the Greek navy. There was no cause for worry, "it was not a god who threatened Greece, but a man. . .the present enemy was no exception; he too was human, and was sure to be disappointed of his great expectations (VII, 203)."
The soldiers from the different groups were under their own regional commander but in over all control at Thermopylae was Leonidas the Spartan. He was the King of Sparta and of the 300 men that he brought they "were chosen by himself, all fathers of living sons (VII, 205)." The Persians waited for four days in their position assuming that the Greeks would run from the superior force before them. On the fifth day Xerxes tired of waiting sent his soldiers to capture the Greeks and bring them back alive. The Medes charged and "many fell; but others took their places...they made it plain enough to anyone, and not least to the king himself, that he had in his army many men, indeed, but few soldiers (VII, 210)." After the regular soldiers failed to take the Greeks Xerxes sent forth the Immortals, 10,000 hand-picked soldiers, to take the pass. But with "the two armies fighting in a confined space, the Persians using shorter spears than the Greeks and having no advantage from their numbers (VII, 211)" they could not take the pass. After two days of charging the pass a man named Ephialtes came to Xerxes with information on how to get the Greeks from behind.