The main source for the battle of 480 is Herodotus, Histories, 7.201-233, which is offered here in the translation by G.C. Macaulay, with adaptations.
[7.202] These were the Greeks who awaited the attack of the Persian in
- of the Spartans three hundred hoplites;
- of the men of Tegea and Mantinea a thousand, half from each place;
- from Orchomenos in Arcadia a hundred and twenty
- from the rest of Arcadia a thousand;
- from Corinth four hundred;
- from Phlius two hundred
- of the men of Mycenae eighty
These were they who came from the Peloponnese; and from the Boeotians
- seven hundred of the Thespians,
- and of the Thebans four hundred.
[7.203] In addition to these, the Locrians of Opus had been summoned to come in their full force, and of the Phocians a thousand: for the Greeks had of themselves sent a summons to them, saying by messengers that they had come as forerunners of the others, that the rest of the allies were to be expected every day, that their sea was safely guarded, being watched by the Athenians and the Aeginetans and by those who had been appointed to serve in the fleet, and that they need fear nothing: for it was not a god, they said, who was coming to attack Greece, but a man; and there was no mortal, nor would be any, with those fortunes evil had not been mingled at his very birth, and the greatest evils for the greatest men; therefore he also who was marching against them, being mortal, would be destined to fail of his expectation. They accordingly, hearing this, came to the assistance of the others at Trachis.
[7.205] For as he had two brothers each older than himself, namely Cleomenes and Dorieus, he had been far removed from the thought of becoming king. Since however Cleomenes had died without male child, and Dorieus was then no longer alive, but he also had brought his life to an end in Sicily, thus the kingdom came to Leonidas, both because was of elder birth than Cleombrotus (for Cleombrotus was the youngest of the sons of Anaxandrides) and also because he had in marriage the daughter of Cleomenes. He then at this time went to Thermopylae, having chosen the three hundred who were appointed by law and men who chanced to have sons; and he took with him besides, before he arrived, those Thebans whom I mentioned when I reckoned them in the number of the troops, of whom the commander was Leontiades the son of Eurymachus. Leonidas was anxious to take up these with him of all the Greeks, because accusations had been strongly brought against them that they were taking the side of the Medes [i.e., Persians]; therefore he summoned them to the war, desiring to know whether they would send troops with them or whether they would openly renounce the alliance of the Greeks; and they sent men, having other thoughts in their mind the while.
[7.206] These with Leonidas the Spartans had sent out first, in order that seeing them, the other allies might join in the campaign, and for fear that they would side with the Medes if they heard that the Spartans were putting off their action. Afterwards, however, when they had kept the festival (for the festival of the Carneia stood in their way), they intended then to leave a garrison in Sparta and to come to help in full force with speed: and just so also the rest of the allies had thought of doing themselves; for it chanced that the Olympic festival fell at the same time as these events. Accordingly, since they did not suppose that the fighting in Thermopylae would so soon be decided, they sent only the forerunners of their force.
[7.207] These had intended to do thus, and meanwhile the Greeks at Thermopylae, when the Persian had come near to the pass, were in dread, and deliberated about making retreat from their position. To the rest of the Peloponnesians then it seemed best that they should go to the Peloponnese and hold the Isthmus in guard; but Leonidas, when the Phokians and Locrians were indignant at this opinion, gave his vote for remaining there, and for sending at the same time messengers to the several states bidding them to come up to help them, since they were but few to repel the army of the Medes.
[7.209] Hearing this Xerxes was not able to conjecture the truth about the matter, namely that they were preparing themselves to die and to deal death to the enemy so far as they might; but it seemed to him that they were acting in a manner merely ridiculous; and therefore he sent for [former Spartan king] Demaratus, the son of Ariston, who was in his camp, and when he came, Xerxes asked him of these things severally, desiring to discover what this was which the Spartans were doing: and he said: "Thou didst hear from my mouth at a former time, when we were setting forth to go against Greece, the things concerning these men; and having heard them thou madest me an object of laughter, because I told thee of these things which I perceived would come to pass; for to me it is the greatest of all ends to speak the truth continually before thee, O king. Hear then now also: these men have come to fight with us for the passage, and this is it that they are preparing to do; for they have a custom which is as follows: whenever they are about to put their lives in peril, they attend to the arrangement of their hair. Be assured however, that if thou shalt subdue these and the rest of them which remain behind in Sparta, there is no other race of men which will await thy onset, O king, or will raise hands against thee: for now thou art about to fight against the noblest kingdom and city of those which are among the Greeks, and the best men." To Xerxes that which was said seemed to be utterly incredible, and he asked again a second time in what manner being so few they would fight with his host. He said; "O king, deal with me as with a liar, if thou find not that these things come to pass as I say."
[7.210] Thus saying he did not convince Xerxes, who let four days go by, expecting always that they would take to flight; but on the fifth day, when they did not depart but remained, being obstinate, as he thought, in impudence and folly, he was enraged and sent against them the Medes and the Cissians, charging them to take the men alive and bring them into his presence. Then when the Medes moved forward and attacked the Greeks, there fell many of them, and others kept coming up continually, and they were not driven back, though suffering great loss: and they made it evident to every man, and to the king himself not least of all, that human beings are many but men are few. This combat went on throughout the day.
[7.212] And during these onsets it is said that the king, looking on, three times leapt up from his seat, struck with fear for his army. Thus they contended then. On the following day the barbarians strove with no better success; for because the men opposed to them were few in number, they engaged in battle with the expectation that they would be found to be disabled and would not be capable any longer of raising their hands against them in fight. The Greeks however were ordered by companies as well as by nations, and they fought successively each in turn, excepting the Phocians, for these were posted upon the mountain to guard the path. So the Persians, finding nothing different from that which they had seen on the former day, retired back from the fight.
[7.213] Then when the king was in a strait as to what he should do in the matter before him, Ephialtes the son of Eurydemos, a Malian, came to speech with him, supposing that he would win a very great reward from the king; and this man told him of the path which leads over the mountain to Thermopylae, and brought about the destruction of those Greeks who remained in that place. Afterwards from fear of the Spartans he fled to Thessaly, and when he had fled, a price was proclaimed for his life by the Deputies, when the Amphictyons met for their assembly at Pylai. Then some time afterwards having returned to Anticyra he was slain by Athenades a man of Trachis. Now this Athenades killed Ephialtes for another cause, which I shall set forth in the following part of the history, but he was honored for it none the less by the Spartans.
[7.214] Thus Ephialtes after these events was slain: there is however another tale told, that Onetes the son of Phanagoras, a man of Carystos, and Corydallos of Anticyra were those who showed the Persians the way round the mountain; but this I can by no means accept: for first we must judge by this fact, namely that the Deputies of the Greeks did not proclaim a price for the lives of Onetes and Corydallos, but for that of Ephialtes the Trachinian, having surely obtained the most exact information of the matter; and secondly we know that Ephialtes was an exile from his country to avoid this charge. True it is indeed that Onetes might know of this path, even though he were not a Malian, if he had had much intercourse with the country; but Ephialtes it was who led them round the mountain by the path, and him therefore I write down as the guilty man.
[7.215] Xerxes accordingly, being pleased by that which Ephialtes engaged to accomplish, at once with great joy proceeded to send Hydarnes and the men of whom Hydarnes was commander; and they set forth from the camp about the time when the lamps are lit. This path of which we speak had been discovered by the Malians who dwell in that land, and having discovered it they led the Thessalians by it against the Phocians, at the time when the Phocians had fenced the pass with a wall and thus were sheltered from the attacks upon them: so long ago as this had the pass been proved by the Malians to be of no value.
[7.218] While the Persians were ascending, they were concealed from these, since all the mountain was covered with oak trees; and the Phocians became aware of them after they had made the ascent as follows: the day was calm, and not a little noise was made by the Persians, as was likely when leaves were lying spread upon the ground under their feet; upon which the Phocians started up and began to put on their arms, and by this time the barbarians were close upon them. These, when they saw men arming themselves, fell into wonder, for they were expecting that no one would appear to oppose them, and instead of that they had met with an armed force. Then Hydarnes, seized with fear lest the Phocians should be Spartans, asked Ephialtes of what people the force was; and being accurately informed he set the Persians in order for battle. The Phocians however, when they were hit by the arrows of the enemy, which flew thickly, fled and got away at once to the topmost peak of the mountain, fully assured that it was against them that the enemy had designed to come, and here they were ready to meet death. These were in this mind; but the Persians meanwhile with Ephialtes and Hydarnes made no account of the Phokians, but descended the mountain with all speed.
[7.219] To the Greeks who were in Thermopylae first the soothsayer Megistias, after looking into the victims which were sacrificed, declared the death which was to come to them at dawn of day; and afterwards deserters brought the report of the Persians having gone round. These signified it to them while it was yet night, and thirdly came the day-watchers, who had run down from the heights when day was already dawning. Then the Greeks deliberated, and their opinions were divided; for some urged that they should not desert their post, while others opposed this counsel. After this they departed from their assembly, and some went away and dispersed each to their several cities, while others of them were ready to remain there together with Leonidas.
[7.221] Of this the following has been to my mind a proof as convincing as any other, namely that Leonidas is known to have endeavoured to dismiss the soothsayer also who accompanied this army, Megistias the Acarnanian, who was said to be descended from Melampus, that he might not perish with them after he had declared from the victims that which was about to come to pass for them. He however when he was bidden to go would not himself depart, but sent away his son who was with him in the army, besides whom he had no other child.
[7.222] The allies then who were dismissed departed and went away, obeying the word of Leonidas, and only the Thespians and the Thebans remained behind with the Spartans. Of these the Thebans stayed against their will and not because they desired it, for Leonidas kept them, counting them as hostages; but the Thespians very willingly, for they said that they would not depart and leave Leonidas and those with him, but they stayed behind and died with them. The commander of these was Demophilos the son of Diadromes.
[7.223] Xerxes meanwhile, having made libations at sunrise, stayed for some time, until about the hour when the market fills, and then made an advance upon them; for thus it had been enjoined by Ephialtes, seeing that the descent of the mountain is shorter and the space to be passed over much less than the going round and the ascent. The barbarians with Xerxes were accordingly advancing to the attack; and the Greeks with Leonidas, feeling that they were going forth to death, now advanced out much further than at first into the broader part of the defile; for when the fence of the wall was being guarded, they on the former days fought retiring before the enemy into the narrow part of the pass; but now they engaged with them outside the narrows, and very many of the barbarians fell: for behind them the leaders of the divisions with scourges in their hands were striking each man, ever urging them on to the front. Many of them then were driven into the sea and perished, and many more still were trodden down while yet alive by one another, and there was no reckoning of the number that perished: for knowing the death which was about to come upon them by reason of those who were going round the mountain, they displayed upon the barbarians all the strength which they had, to its greatest extent, disregarding danger and acting as if possessed by a spirit of recklessness.
[7.227] This and other sayings of this kind they report that Dieneces the Spartan left as memorials of himself; and after him the bravest they say of the Spartans were two brothers Alpheus and Maron, sons of Orsiphantos. Of the Thespians the man who gained most honour was named Dithyrambos son of Harmatides.
[7.229] Two of these three hundred, it is said, namely Eurystus and Aristodemus, who, if they had made agreement with one another, might either have come safe home to Sparta together (seeing that they had been dismissed from the camp by Leonidas and were lying at Alpenoi with disease of the eyes, suffering extremely), or again, if they had not wished to return home, they might have been slain together with the rest - when they might have done either one of these two things, would not agree together; but the two being divided in opinion, Eurystus, it is said, when he was informed that the Persians had gone round, asked for his arms and having put them on ordered his helot to lead him to those who were fighting; and after he had led him thither, the man who had led him ran away and departed, but Eurystus plunged into the thick of the fighting, and so lost his life: but Aristodemus was left behind fainting. Now if either Aristodemus had been ill alone, and so had returned home to Sparta, or the men had both of them come back together, I do not suppose that the Spartans would have displayed any anger against them; but in this case, as the one of them had lost his life and the other, clinging to an excuse which the first also might have used, had not been willing to die, it necessarily happened that the Spartans had great indignation against Aristodemus.
[7.230] Some say that Aristodemus came safe to Sparta in this manner, and on a pretext such as I have said; but others, that he had been sent as a messenger from the camp, and when he might have come up in time to find the battle going on, was not willing to do so, but stayed upon the road and so saved his life, while his fellow-messenger reached the battle and was slain.
[7.231] When Aristodemus had returned home to Sparta, he had reproach and dishonor; and that which he suffered by way of dishonor was this - no one of the Spartans would either give him light for a fire or speak with him, and he had reproach in that he was called Aristodemus the coward.
[7.232] He however in the battle at Plataea repaired all the guilt that was charged against him: but it is reported that another man also survived of these three hundred, whose name was Pantites, having been sent as a messenger to Thessaly, and this man, when he returned back to Sparta and found himself dishonored, is said to have strangled himself.
[7.234] Thus did the Greeks at Thermopylae contend in fight.