Herodotus writes of the Battle at Thermopylae

[7.175] [As the Persian force approached Hellas] the Hellenes...consulted as to...how they should make a stand for war, and in what places. And the opinion which won out was that they should guard the pass at Thermopylae...and that the fleet should sail...to Artemesion. For these places are near to one another so that each force would be able to learn how the other was doing....

[7.176] ....At Thermopylae on the side towards evening [= the West] is a mountain, unpassable and very steep, an extension of Mt. Oita; and on the side of the road towards the dawn there lies sea and shallows. (There are in this pass warm bathing pools....)

[7.204] ...[When the Hellenes gathered at Thermopylae, each contingent had its own general] but the most highly regarded one, and the leader of the whole army, was the Lakedaimonian Leonidas son of Anaxandrides...[a descendant of] Herakles; and he was a king in Sparta....

[7.207] ...The Hellenes at Thermopylae, when the Persian was near the pass, grew afraid and began discussing a withdrawal. Now to the other Peloponnesians it seemed best to return to the Peloponnese and to hold that isthmus under guard. But Leonidas, when the Phokians and Lokrians expressed anger at this opinion, voted to remain there and to send messengers to the other poleis commanding them to come and help, since the ones there were too few to ward off the army of the Persians.

[7.208] While they were discussing these things, Xerxes sent a scout, a mounted one, to see how many they were and what they were doing...and he examined the ones outside, the ones whose arms lay in front of the wall. It happened that at that time the Lakedaimonians were stationed outside. Of these, the scout saw some men exercising naked and others combing their hair. Seeing these things he marveled, and took note of their number; and when he had noted everything exactly he departed and went back in peace (for no one pursued him and he met with great indifference).

[7.209] And, going away, he told Xerxes all he had seen. When Xerxes heard it, he did not understand the reality, that the Lakedaimonians were preparing to be slain or to slay as far as they were able; but to him they appeared to be doing laughable things, and he sent for Demaretos son of Aristos [a Hellene] who was in his army-camp. When the man came Xerxes asked him about each of these things, wishing to understand what was done by the Lakedaimonians, and he said: "You have heard before from me, when we were setting out against Hellas, concerning these men; but hearing, you laughed at me when I said how I saw this business would turn out....But listen even now: these men are come to fight us for the road into Hellas, and for that they are preparing. For custom holds among them thus: when they are about to risk their lives, then they dress their hair. And know this: if you overcome these and the force which remains in Sparta, there is no other race of men, o king, which will abide you when against them you raise up your hand. For now against the best royalty and polis of the ones in Hellas you are bringing yourself, and against the best men."

And indeed to Xerxes what he said appeared untrustable....

[7.219] [When the Persians were shown, by a traitor, a route around the pass], to the Hellenes in Thermopylae first the prophet Megistes, when he had examined the sacrificial offerings, said that there would come, together with the dawn, death; and after that also came deserters who announced the Persian circumvention....Then the Hellenes held council, and their opinions were divided, some holding that they should not leave their station, others opposing this; and after that they divided themselves, some going away and dispersing, turning back each to their own poleis, but others of them were prepared to remain there with Leonidas.

[7.220] And it is said that Leonidas himself sent them away, caring lest they be destroyed but for himself and the Spartans present not holding it as fitting that they should leave that station which they had come to guard at first. But on this subject I am rather more of the opinion that Leonidas, when he saw the allies not enthusiastic and not willing to run the risk with him, ordered them to withdraw, retreat for himself not being honorable; if he stayed, he would leave his own great fame, and Sparta's prosperity would not be eclipsed. For there was an oracle, given by the Pythian [priestess at Delphi] to the Spartans when they asked about this war just when it began—that either Lakedaimonia would be destroyed by the barbaroi or a king of theirs must die....It is my opinion that Leonidas considered this and wishing that the Spartans alone [or, "that he alone of the Spartans"] should get the fame, he sent away the allies....

[7.223] And the Hellenes with Leonidas, since it was to death that they were making their march, now much further than at first went out into the wider part of the pass....and then when they engaged the enemy outside the narrows there fell in a multitude many of the barbaroi (for behind them the leaders of their companies with whips kept striking every man, ever driving them forward). Many of them indeed fell into the sea and perished, while many more still were trampled alive by each other; and there was no reckoning of who was dying. For, because they knew that for them was coming death at the hands of the men coming around the mountain, the Hellenes exhibited as much strength as they possessed against the barbaroi and were contemptuous [of death] and also reckless.

[7.224] The spears now of the most of them by this time had broken, but they used their swords to slay the Persians. And Leonidas in that toil fell—a man become heroic—and others with him, the most renowned of the Spartans....[and the entire Hellenic force still at Thermopylae].

[7.226] ...It is said that the man who was bravest was the Spartan Dienekes. They say that this man told a story that before they engaged themselves with the Persians he had heard from one of the [enemy] Trachinians that when the barbaroi shot off their bows, the very sun by the multitude of arrows would be hidden away, such was the multitude of them. But he, not dismayed by these things, said (making light of the Persian multitude), "all things for us are good, which the Trachinian stranger reports—if the Persians hide away the sun, then in the shade we will fight them and not in the sunlight."
....

[7.228] And they were buried there in the very spot where they fell, and with them those who had died before some had been by Leonidas sent away; and written over them are letters saying the following:

Against three million, once, here fought
from the Peloponnese, four thousand.
This indeed is written over them all; but for the Spartans privately,
O stranger, announce to the Lakedaimonians that here
we lie, to their words obedient.