Xerxes assembled a vast army for the invasion of Greece. Faced with this threat, the Athenians and Spartans forgot their differences and united under a Spartan command. The original plan was to stop the Persians at the Tempe Gorge, a narrow pass at the south end of Mount Olympus. Fearing being bypassed the Greeks withdrew. The nothern towns feared they were to be abandoned , submitted to the Persians. To stop any further defections, the Greeks decided to make a stand at Thermopylae. Named after the hot thermal springs near the village of Thermopylae.
Here the narrow coastal pass is flanked on oneside by steep mountains, on the other by the sea. The pass narrows in several places, it is at the middle gate, where previously a defence wall was built, that the Greeks made there stand.
The Greek force consisted of the Spartan King, Leonidas and his body guard of 300, 2,800 Peloponnesians and approximately 900 helots. they were joined by 700 Thespians, 400 Thebans, 1,000 Phocians and the complete army of Locrians. The soldiers being told that they were the advance guard and the rest of the army would join them.
The Persians launched a series of assaults on the Greeks. First the Medes, commanded by Tigranes, assaulted with some enthusiasm but very driven back with considerable losses. Then Xerxes sent in the men from Susa, these were heavily armoured with large shields, but even so, they too were no match for the Spartans. They even tried work their way around the coastal flank but with no success, their bodies falling into the sea. Xerxes frustration was evident, as a last resort then ordered the Immortals forward. As the Immortals advanced, the Spartans moved from their defensive position behind the wall and advanced to meet them. The Immortals fought in good order no were not equal to the well drilled hoplites with their long spears. The Spartans, confident in their ability to handle the best of the Persian army, feinted a retreat, The Immortals followed up quickly only to be caught in disorder as they collided with a Spartan line as it turned to face. The Immortals were also forced to withdraw, ending the first day of fighting.
The second day of fighting was no better for the Persians, the troops were now disheartened by their losses and lack of progress. The narrow front limited the number of troops that could be engaged but allowed the persians to withdraw and rest while a fresh wave of troops attacked. However the Greek line also organised a regular changeover of hoplites which allowed them to rest and tend their wounds. By the end of the second day, Leonidas still held the pass but it seemed that no reinforcements were coming.
The Persians now had some luck. Ephialtes, a local Greek peasant, informed the Persians of a route that would allow them to outflank the Greeks. Hydarnes led his Immortals out of camp as soon as it was dark. Marching all night along the winding mountain path, the Immortals came across the guard of 1,000 Phocians in the early morning. Showered with arrows, the Phocians withdrew to the hill top but this allowed the Immortals a clear passage.
The Greeks received news of the Immortals movements and Leonidas allows those Greek who wish to withdraw to do so. The 700 Thespians and 400 Thebans remained. Xerxes held back his attack until mid morning, giving the Immortals time to get into position. As the Persians advanced on the Greek position, again the Greeks advanced to where the pass widened. here they deployed in normal phalanx formation with the lightly armed helots covering the flanks. The struggle was bloody with Persians having to scamble over the bodies of the fallen to reach the Spartans. It is here that Leonidas was killed, the battle raged over his corpse. Four times the Persians captured it, four times it was dragged back. The struggle continued until news came that the Immortals arrival. The Greeks withdrew back over the defence wall and to a small hillock. There they formed a circle, armed now only with their swords, their spears having been broken on the enemy. They fought on, sometimes only with their hands. Eventually being overwhelmed by missile fire. By midday of the third day, all was quiet.