In the spring of 480 bc, Xerxes put his great plan in motion. The Persian army crossed the Hellespont and, with the Persian fl eet following just off - shore, marched unopposed along the northern coast of the Aegean Sea through Thrace and Macedonia before turning south into Thessaly. The Persians sought to bring the Greeks to batt le, destroy their armies, and end the war quickly. The large and slow- moving Persian host, however, did not run into the first Greek defensive line until reaching the narrow pass of Thermopylae in central Greece. There a picked force of three hundred men under Spartan king Leonidas, joined by six thousand additional hoplites from other Greek cities and supported by the Greek fleet off shore, defended the pass. The Spartan defensive position and shield wall represented an intimidating obstacle. The clash of arms began badly for the Persians. Xerxes’ navy, unable to find a harbor large enough for the entire fleet, lost hundreds of ships and innumerable crewmen in a three- day gale just before the battle. Over the course of three days off the coast of the town of Artemisium on Euboea, the Persians were stymied in a series of small naval battles with the Greeks and were prevented from making an amphibious landing behind the Spartan position. Unable to find a way around the Spartans, Xerxes launched several costly and unsuccessful frontal assaults on Leonidas’s position. No match for the Greeks in man- to- man combat, the Medes and then the Immortals broke like waves on the Spartan shield wall and were badly mauled. The Persian cavalry, Xerxes’ main off ensive arm, lacked the room to deploy and stood by idly watching the contest.