For you 300 fans (whose ranks I hope to join soon once I see the flick), the account of the Battle at the Pass of Thermopylae. From Herodotus’ The Persian Wars (Bk VII.201-234)
[7.201] King Xerxes pitched his camp in the region of Malis called Trachinia, while on their side the Greeks occupied the straits. These straits the Greeks in general call Thermopylae (the Hot Gates); but the natives, and those who dwell in the neighbourhood, call them Pylae (the Gates). Here then the two armies took their stand; the one master of all the region lying north of Trachis, the other of the country extending southward of that place to the verge of the continent.
[7.202] The Greeks who at this spot awaited the coming of Xerxes were the following:- From Sparta, three hundred men-at-arms; from Arcadia, a thousand Tegeans and Mantineans, five hundred of each people; a hundred and twenty Orchomenians, from the Arcadian Orchomenus; and a thousand from other cities: from Corinth, four hundred men; from Phlius, two hundred; and from Mycenae eighty. Such was the number from the Peloponnese. There were also present, from Boeotia, seven hundred Thespians and four hundred Thebans.
[7.203] Besides these troops, the Locrians of Opus and the Phocians had obeyed the call of their countrymen, and sent, the former all the force they had, the latter a thousand men. For envoys had gone from the Greeks at Thermopylae among the Locrians and Phocians, to call on them for assistance, and to say – “They were themselves but the vanguard of the host, sent to precede the main body, which might every day be expected to follow them. The sea was in good keeping, watched by the Athenians, the Eginetans, and the rest of the fleet. There was no cause why they should fear; for after all the invader was not a god but a man; and there never had been, and never would be, a man who was not liable to misfortunes from the very day of his birth, and those misfortunes greater in proportion to his own greatness. The assailant therefore, being only a mortal, must needs fall from his glory.” Thus urged, the Locrians and the Phocians had come with their troops to Trachis.
[7.204] The various nations had each captains of their own under whom they served; but the one to whom all especially looked up, and who had the command of the entire force, was the Lacedaemonian, Leonidas. Now Leonidas was the son of Anaxandridas, who was the son of Leo, who was the son of Eurycratidas, who was the son of Anaxander, who was the son of Eurycrates, who was the son of Polydorus, who was the son of Alcamenes, who was the son of Telecles, who was the son of Archelaus, who was the son of Agesilaus, who was the son of Doryssus, who was the son of Labotas, who was the son of Echestratus, who was the son of Agis, who was the son of Eurysthenes, who was the son of Aristodemus, who was the son of Aristomachus, who was the son of Cleodaeus, who was the son of Hyllus, who was the son of Hercules.
Leonidas had come to be king of Sparta quite unexpectedly.
[7.205] Having two elder brothers, Cleomenes and Dorieus, he had no thought of ever mounting the throne. However, when Cleomenes died without male offspring, as Dorieus was likewise deceased, having perished in Sicily, the crown fell to Leonidas, who was older than Cleombrotus, the youngest of the sons of Anaxandridas, and, moreover, was married to the daughter of Cleomenes. He had now come to Thermopylae, accompanied by the three hundred men which the law assigned him, whom he had himself chosen from among the citizens, and who were all of them fathers with sons living. On his way he had taken the troops from Thebes, whose number I have already mentioned, and who were under the command of Leontiades the son of Eurymachus. The reason why he made a point of taking troops from Thebes, and Thebes only, was that the Thebans were strongly suspected of being well inclined to the Medes. Leonidas therefore called on them to come with him to the war, wishing to see whether they would comply with his demand, or openly refuse, and disclaim the Greek alliance. They, however, though their wishes leant the other way, nevertheless sent the men.
[7.206] The force with Leonidas was sent forward by the Spartans in advance of their main body, that the sight of them might encourage the allies to fight, and hinder them from going over to the Medes, as it was likely they might have done had they seen that Sparta was backward. They intended presently, when they had celebrated the Carneian festival, which was what now kept them at home, to leave a garrison in Sparta, and hasten in full force to join the army. The rest of the allies also intended to act similarly; for it happened that the Olympic festival fell exactly at this same period. None of them looked to see the contest at Thermopylae decided so speedily; wherefore they were content to send forward a mere advanced guard. Such accordingly were the intentions of the allies.