Battle of Thermopylae at Thermopylae, the Persians sent a mounted scout to reconnoitre. The Greeks allowed him to come up to the camp, observe them, and depart. Xerxes found the scout's reports of the size of the Greek force, and that the Spartans were indulging in callisthenics and combing their long hair, laughable. Seeking the counsel of Demaratus, an exiled Spartan king in his retinue, Xerxes was told the Spartans were preparing for battle, and it was their custom to adorn their hair when they were about to risk their lives. Demaratus called them "the bravest men in Greece" and warned the Great
Delian League to the Persian Empire, and Eretria was duly destroyed. However, the invasion ended in 490 BC with the decisive Athenian victory at the Battle of Marathon. Between the two invasions, Darius died, and responsibility for the war passed to his son Xerxes I. Xerxes then personally led a second Persian invasion of Greece in 480 BC, taking an enormous (although oft-exaggerated) army and navy to Greece. Those Greeks who chose to resist (the 'Allies') were defeated in the twin simultaneous battles of Thermopylae on land and Artemisium at sea. All of Greece except the Peloponnesus thus having fallen into Persian