For, as he had two elder brothers, Cleomenes and Dorieus, he was far from any thought of the kingdom. However, Cleomenes having died without male issue, and Dorieus being no longer alive—having ended his days in Sicily—the kingdom thus devolved upon Leonidas; both because he was older than Cleombrotus—for he was the youngest son of Anaxandrides—and also because he had married the daughter of Cleomenes. He then marched to Thermopylæ, having chosen the three hundred men allowed by law, and such as had children. On his march he took with him the Thebans, whose numbers I have already reckoned, and whom Leontiades, son of Eurymachus, commanded. For this reason Leonidas was anxious to take with him the Thebans alone of all the Greeks, because they were strongly accused of favoring the Medes: he therefore summoned them to the war, wishing to know whether they would send their forces with him, or would openly renounce the alliance of the Grecians; but they, though otherwise minded, sent assistance.
The Spartans sent these troops first with Leonidas, in order that the rest of the allies, seeing them, might take the field, and might not go over to the Medes if they heard that they were delaying; but afterward—for the Carnean festival was then an obstacle to them—they purposed, when they had kept the feast, to leave a garrison in Sparta and to march immediately with their whole strength. The rest of the confederates likewise intended to act in the same manner; for the Olympic games occurred at the same period as these events. As they did not, therefore, suppose that the engagement at Thermopylæ would so soon be decided, they despatched an advance-guard.
The Greeks at Thermopylæ, when the Persians came near the pass, being alarmed, consulted about a retreat; accordingly, it seemed best to the other Peloponnesians to retire to Peloponnesus, and guard the Isthmus; but Leonidas, perceiving the Phocians and Locrians were very indignant at this proposition, determined to stay there, and to despatch messengers to the cities, desiring them to come to their assistance, they being too few to repel the army of the Medes.
While they were deliberating on these matters, Xerxes sent a scout on horseback, to see how many they were and what they were doing; for while he was still in Thessaly, he had heard that a small army had been assembled at that spot, and as to their leaders, that they were Lacedæmonians, and Leonidas, who was of the race of Hercules. When the horseman rode up to the camp, he reconnoitred, and saw not indeed the whole camp, for it was not possible that they should be seen who were posted within the wall, which having rebuilt they were now guarding; but he had a clear view of those on the outside, whose arms were piled in front of the wall. At this time the Lacedæmonians happened to be posted outside; and some of the men he saw performing gymnastic exercises, and others combing their hair. On beholding this he was astonished, and ascertained their number, and having informed himself of everything accurately, he rode back at his leisure, for no one pursued him and he met with general contempt. On his return he gave an account to Xerxes of all that he had seen.
When Xerxes heard this, he could not comprehend the truth that the Grecians were preparing to be slain and to slay to the utmost of their power; but, as they appeared to behave in a ridiculous manner, he sent for Demaratus, son of Ariston, who was then in the camp, and when he was come into his presence Xerxes questioned him as to each particular, wishing to understand what the Lacedæmonians were doing. Demaratus said: "You before heard me when we were setting out against Greece, speak of these men, and when you heard, you treated me with ridicule though I told you in what way I foresaw these matters would issue; for it is my chief aim, O king, to adhere to the truth in your presence; hear it, therefore, once more. These men have to fight with us for the pass and are now preparing themselves to do so; for such is their custom when they are going to hazard their lives, then they dress their heads; but be assured if you conquer these men and those that remain in Sparta, there is no other nation in the world that will dare to raise its hand against you, O king! for you are now to engage with the noblest kingdom and city of all among the Greeks and with the most valiant men." What was said seemed incredible to Xerxes and he asked again, "how, being so few in number, they could contend with his army." He answered: "O king, deal with me as with a liar if these things do not turn out as I say!"
By saying this he did not convince Xerxes. He therefore let four days pass, constantly expecting that they would be taking themselves to flight; but on the fifth day, as they had not retreated, but appeared to him to stay through arrogance and rashness, he, being enraged, sent the Medes and Cissians against them, with orders to take them alive, and bring them into his presence. When the Medes bore down impetuously upon the Greeks, many of them fell; others followed to the charge, and were not repulsed, though they suffered greatly; but they made it evident to every one, and not least of all to the king himself, that they were indeed many men, but few soldiers. The engagement lasted through the day.
When the Medes were roughly handled, they thereupon retired, and the Persians whom the king called "Immortal," and whom Hydarnes commanded, taking their place advanced to the attack thinking that they indeed would easily settle the business. But when they engaged with the Grecians they succeeded no better than the Medic troops, but just the same; as they fought in a narrow space and used shorter spears than the Greeks, they were unable to avail themselves of their numbers. The Lacedæmonians fought memorably in other respects, showing that they knew how to fight with men who knew not, and whenever they turned their backs they retreated in close order, but the barbarians, seeing them retreat, followed with a shout and clamor; then they, being overtaken, wheeled round so as to front the barbarians, and having faced about, overthrew an inconceivable number of the Persians, and then some few of the Spartans themselves fell, so that when the Persians were unable to gain anything in their attempt on the pass by attacking in troops and in every possible manner, they retired.
It is said that during these onsets of the battle, the king, who witnessed them, thrice sprang from his throne, being alarmed for his army. Thus they strove at that time. On the following day the barbarians fought with no better success; for considering that the Greeks were few in number, and expecting that they were covered with wounds and would not be able to raise their heads against them any more, they renewed the contest. But the Greeks were marshalled in companies and according to their several nations, and each fought in turn, except only the Phocians; they were stationed at the mountain to guard the pathway. When, therefore, the Persians found nothing different from what they had seen on the preceding day, they retired.
While the king was in doubt what course to take in the present state of affairs, Ephialtes, son of Eurydemus, a Malian, obtained an audience of him (expecting that he should receive a great reward from the king), and informed him of the path which leads over the mountain to Thermopylæ, and by that means caused the destruction of those Greeks who were stationed there; but afterward, fearing the Lacedæmonians, he fled to Thessaly, and when he had fled, a price was set on his head by the Pylagori when the Amphictyons were assembled at Pylæ; but some time after, he went down to Anticyra and was killed by Athenades, a Trachinian.
Another account is given, that Onetes, son of Phanagoras, a Carystian, and Corydallus of Anticyra, were the persons who gave this information to the king and conducted the Persians round the mountains; but to me, this is by no means credible; for, in the first place, we may draw the inference from this circumstance, that the Pylagori of the Grecians set a price on the head, not of Onetes and Corydallus, but of Ephialtes the Trachinian, having surely ascertained the exact truth; and, in the next place, we know that Ephialtes fled on that account. Onetes, indeed, though he was not a Malian, might be acquainted with this path if he had been conversant with the country; but it was Ephialtes who conducted them round the mountain by the path, and I charge him as the guilty person.