The movie 300 is an exaggerated retelling of the Battle of Thermopylae. While the characters and many the events were real, a lot of the facts in the movie were exaggerated for dramatic effect. In other words, the film is semi-authentic it tells a story that really happened but it is not a reliable record of the true events.
The first and most glaring exaggeration can be found in the trailer which goes “Three Hundred against One Million”. This suggests that the Greeks were utterly outnumbered. In truth the Greek army was much smaller than the Persian army but the true number were around 7000 Greeks against 100,000 to 300,000, the true number is still subject to debate, Persians. Also while Spartans were prominent in the real battle of Thermopylae the 300 Spartans did not go at it alone, there were soldiers from the other Greek city-states, Athens, Thespia, Thebes and the others joined the Spartans for perhaps the first time in defense of Greece against their common foe. In the movie version the Spartans were alone except for a handful of amateurs. This exaggeration made the Spartans stand more amazing to the movie-goers.
The second obvious difference is the attire of the Spartans. In the movie the Spartans wore fur briefs, a red cape, helmet and little else. In reality, the Spartans fought as Hoplites. In addition to the helmet, shield and spear they had in the movie, the Hoplites also wore heavy bronze armor and it is unlikely the ordinary Spartan soldiers had long red capes like they did in the movie since the capes served no function in battle and would only make it harder for the Spartans to move.
The battle sequences were also exaggerated the Spartans, while really good soldiers, probably were not as dominating as they were in the movie. For example, during the first battle it looked like every time a Spartan and a Persian met the Persian was doomed and all he could do is die. There were no elephants in the Xerxes’ army and it is very unlikely that he had bomb throwers. The ‘fight in the shade’ scene is true. The Persians had so many archers that when they fired on the Greeks it looked like they blotted out the sun. Since the Greeks had heavy armor and shield, the arrows had no effect.
The Immortals were not the freakish force of monsters with ‘eyes dark as night, teeth filed into fangs’. But they were Xerxes personal guard and the Persian warrior elite. The Immortals were probably the deadliest fighting force in Asia. They were Medes from the Persian province where Xerxes came from and were an elite force of 10,000 of the best soldiers in his army. But they did not wear the evil-looking armor, instead they wore clothes that were similar to the regular Persian except theirs was nicer.
‘The world will know that few stood against many’ is mentioned at the end of the trailer and that is truth. On the third day the real-life Ephialtes, but there is no proof that he was a deformed monster, betrayed them and the Spartans remained with the Thebans and Thespians to form a rear-guard while the rest of the Army fled. Around 1,500 in total they stood against the Persians and were slaughtered to the last man, except for the Thebans which allegedly switched sides. Even at their full strength the Greeks were just a fraction of the Persian hordes. The sacrifice at Thermopylae inspired the Greeks and made victory possible later. The movie exaggerates many of the events but it does so to do justice to the courage and sacrifice of the Spartans.