"People of Sparta, either your city is destroyed by the Persians or it is not, and Lakedaimon will mourn a dead king of the Haraklid line. For the might of bulls and lions will not stay the enemy in battle; he has Zeus' might. And I say that he will not stop until he has destroyed one of these two." -Q152, Oracle of Delphi to the Spartans, regarding the Persian invasion (481/480 BC) [Herodotus, 7.220.3-4]Other items of possible interest, regarding the battle itself:
"Do not stay; fly to the ends of the earth, leaving your houses and city. For the whole body is unsound; nothing is left. Fire and war destroy it. Many fortresses will be destroyed, not yours alone. Many temples will burn, and blood drips upon their roofs, presaging inevitable evil. Leave the adyton and be ready for woes." -Q146, Oracle of Delphi to the Athenians, regarding the Persian invasion of the Hellas (481/480 BC)
"Pallas cannot appease Zeus with her many prayers. But I shall tell you this immovable decree: all Attica will be taken, but Zeus grants Athena a wooden wall that shall alone be untaken and will help you and your children. Do not await the onset of cavalry and infantry from the continent at your ease, but turn about and leave. You will face them sometime again. O divine Salamis, you will lose many children of men either at sowing time or at harvest." -Q147, Oracle of Delphi to the Athenians, regarding Oracle Q146 (481/480 BC)¹
Demaratus, a king of Sparta in exile (the Spartans had two kings at a time, not just one), defected to the Persians. He told Xerxes early on:
When the Spartans fight singly they are as brave as any man, but when they fight together they are supreme above all. For though they are free men, they are not free in all respects; law is the master whom they fear, a great deal more than their subjects fear you. They do what the law commands and its command is always the same, not to flee in battle whatever the number of the enemy, but to stand and win, or die."A countryman of Xerxes apparently once asked:
"Why, O God, have you taken upon you the form of a Persian man, changing your name to Xerxes, in order to lead the whole world to conquer and devastate Greece? You could have destroyed Greece without all that trouble."When Xerxes crossed the Hellespont, his first floating bridge was destroyed. Xerxes ordered that the sea be lashed 300 times, that fetters be thrown into the sea, and that the sea be branded as a criminal. The men wielding the whips were ordered to say the following:
"You salt and bitter current, your master inflicts this punishment upon you for doing harm to him, who never harmed you. Nevertheless, Xerxes the King will cross you with or without your permission. No man makes sacrifice to you, and for this neglect you deserve your neglect because of your salty and dirty water."Oh, and he had the bridge designers executed.
The Phocians held the goat path, and they did, indeed, flee the advance of the Immortals without putting up a fight. But I would point out that the Thebans and the Thespians, as well as the Spartan Helots, all remained on the last day. The estimate of how many men occupied the pass on the final day is approximately 2,000: 300 Spartans and the rest Helots, Thespians, and Thebans. Leonidas started the battle with approximately 7,000 men (from Sparta, Thespiae, Thebes, Arcadia, Opus, Phocis, and Malis).
Also, I found this test on the battles of Marathon, Thermopylae, and Salamis and felt that it was good that teachers were actually teaching this stuff.
And FYI, the final battle in the movie 300 is the Battle of Plataea. I admit to being somewhat surprised that the Battle of Artemisium wasn't mentioned, because, you know, that's why the Persian fleet couldn't just sail around Leonidas and take care of business.
Source for everything in the LJ cut (i.e. everything but the Oracle quotes)? Bradford, Ernle. Thermopylae: The Battle for the West. De Capo Press. 1993.
¹ - Source: Fonternrose, Joseph. The Delphic Oracle: Its responses and Operations With a Catalogue of Responses. University of California Press. 1981