The army that the 300 stood up against, was that of Xerxes, King of Persia (which is present-day Iran). The size of that Persian Army was variously guessed as being between 50,000 and a million. While I doubt the latter figure, the biggest problem would be logistics for that army, simply keeping them fed. How does even one of the mightiest powers of 480 BC, manage to move that many soldiers and all their supply lines, over a distance of well over a thousand miles, from Persia to the Greek archipeligo? Now if Xerxes was staging from Asia Minor, a much larger army could be moved in a relatively short time, but still well short of the million or so that was being referred to.
The 300 Spartans under Leonidias that kept the entire Persian army bottled up has to stand as one of the most effective delaying tactics of all time.
If you have cable or a dish network, check out the History Channel. It has been running "Last Stand of the 300" at various times over the last week. It was a great show about the Battle of Thermopylae, giving the facts about the situation, and showing where the movie took a bit of creative license, but apparently not TOO much.
Superior training helps; when you're fighting for something you believe strongly in, such as freedom, you also tend to fight quite hard.
Proving what, that dying hard is better than being just plain dead?
Wars are madness made manifest; peace is surrender and the bad guys will rule forever.
Bring on the global warming and the chips.
The persians built a bridge of ships roped together across the straits of Maramar to avoid having to round the Black sea. It was one the greatest feats of engineering for the period. It saved the army a 2 year march.
The battle of thermopoly was larger than the story you might get in a general history class. It also was a great navel battle, that prevented xerzies armys from completeing a navel flanking manuveur.
Had the warriors of the city state that was supposed hold the rear pass not fled they may have been able to hold the termopoly pass indefinatly.