Second Day

On the second day, Xerxes again sent in the infantry to attack the pass, "supposing that their enemies, being so few, were now disabled by wounds and could no longer resist." However, the Persians had no more success on the second day than on the first. Xerxes at last stopped the assault and withdrew to his camp, "totally perplexed".

Later that day, however, as the Persian king was pondering what to do next, he received a windfall; a Trachinian named Ephialtes informed him of the mountain path around Thermopylae and offered to guide the Persian army. Ephialtes was motivated by the desire for a reward. For this act, the name "Ephialtes" received a lasting stigma; it came to mean "nightmare" in the Greek language and to symbolize the archetypal traitor in Greek culture.

Herodotus reports that Xerxes sent his commander Hydarnes that evening, with the men under his command, the Immortals, to encircle the Greeks via the path. However, he does not say who those men were. The Immortals had been bloodied on the first day, so it is possible that Hydarnes may have been given overall command of an enhanced force including what was left of the Immortals; according to Diodorus, Hydarnes had a force of 20,000 for the mission. The path led from east of the Persian camp along the ridge of Mt. Anopaea behind the cliffs that flanked the pass. It branched, with one path leading to Phocis and the other down to the Malian Gulf at Alpenus, the first town of Locris.

• Outline of the Battle of Thermopylae (480 BC)
  

  HISTORIC BATTLES

  Battle of Thermopylae (480 BC)

  The Battle of Thermopylae was fought between an alliance of Greek city-states, led by King Leonidas of Sparta, and the Persian Empire of Xerxes I over the course of three days, during the second Persian invasion of Greece. View Historic Battle »

  Sources: George B. Grundy was the first modern historian to do a thorough topographical survey of the narrow pass at Thermopylae, and to the extent that modern accounts of the battle differ from Herodotus' they usually follow Grundy's.

  Background: Darius also saw the opportunity to expand his empire into the fractious world of Ancient Greece.

  Prelude: Leonidas took with him the 300 men of the royal bodyguard, the Hippeis. This expedition was to try to gather as many other Greek soldiers along the way as possible and to await the arrival of the main Spartan army.

  Strategic and tactical considerations: From a strategic point of view, by defending Thermopylae, the Greeks were making the best possible use of their forces. As long as they could prevent further a Persian advance into Greece, they had no need to seek a decisive battle and could, thus, remain on the defensive.

  First day battle: First, he ordered 5,000 archers to fire a barrage of arrows, but they were ineffective; they fired from at least 100 yards away, according to modern day scholars, and the Greeks' bronze shields and helmets deflected the missile.

  Second day battle: On the second day, Xerxes again sent in the infantry to attack the pass, "supposing that their enemies, being so few, were now disabled by wounds and could no longer resist." However, the Persians had no more success on the second day than on the first.

  Third day battle: Upon discovering that his army had been encircled, Leonidas told his allies that they could leave if they wanted to. While many of the Greeks took him up on his offer and fled, around two thousand soldiers stayed behind to fight and die.

  Aftermath: With Thermopylae now opened to the Persian army, the continuation of the blockade at Artemisium by the Greek fleet became irrelevant.

RESOURCES
This article uses material from the Wikipedia article "Battle of Thermopylae", which is released under the Creative Commons Attribution-Share-Alike License 3.0.