Pretty meh.

Our main source for the Persian Wars is Herodotus, whose work The Histories deals with the subject. Unfortunately, Herodotus is not the most reliable source ever written, but it does give us some useful information nevertheless.

What we do know is that c.20,000 Greek soldiers, fought a Persian army that numbered somewhere between 70,000 - 300,000 men at Thermopylae for three days in 480BCE. Thermopylae was chosen because it was a natural chokepoint, not as narrow as it is in the film, but still small enough for the Persians not to be able to use their numbers.

The Greeks would have fought in a line, as this was how they fought their warfare. The hoplites would form a phalanx, as this would present both a shield wall and a row of spears. We're not entirely sure how two phalanxes would have fought each other, whether it would have been a physical pushing match or something else (we have no contemporary sources that describe or show this).

One part that the film does not show is the other combatants. There were 300 Spartan hoplites, and they were led by King Leonidas, but there were at least 900 other troops from Lacedaemonia (the region Sparta is in), as well as contingencies from other Greek city-states such as c.700 Thespians and c.400 Corinthians. On the third day of fighting, most of these troops retreated whilst the Spartans stayed behind to provide a rearguard, but some such as the Thespians also remained to the man, and the final vanguard was made up of c.2000 men instead of the 300 shown in the film.

The whole Queen Gorgo bit never happened as well.

The famous quotes, "Come and get them!", "We shall fight them in the shade" are recorded by Herodotus even if they are paraphrased a bit in the film.

Aristodemus (Dilios in the film) was sent back to Sparta, and did fight in the Battle of Plataea where he died. He was not however a hero, he was regarded as a coward upon his return to Sparta. He somewhat redeemed himself at Plataea, fighting ferociously, but he was never regarded in the same light as those who died at Thermopylae.

It is also important to remember that the battle of Thermopylae was a resounding defeat for the Greek forces. Whilst they delayed the Persian force by three days, Athens, Plataea, Thespiae and other cities were sacked and razed. It was not until the naval battle at Salamis later in 480BCE and the battle at Plataea in 479BCE that the Greeks were able to drive the Persians out of Greece. And it would not be until Alexander the Great conquered Persian over 100 years later that the Persians would stop being a major player in Greek politics. Indeed in the Peloponnesian War (431-404BCE), both the Athenians and Spartans would try and covet Persia to help them in their own endeavours.