For all its embellishments and exaggerations, the movie 300 tells you the basics of the Battle of Thermopylae more or less as we know them. A Greek army of about 7,000 led by the Spartan king Leonidas held the pass of Thermopylae against the invading Persian army. For two days they managed to hold their ground despite the Persians' best efforts to dislodge them. On the night of the second day, however, the Persians sent their Immortals up a mountain path to turn the pass. Hearing about their manoeuvre, the Greeks abandoned their now hopeless position, but Leonidas and his detachment of 300 Spartans decided to stay. They were surrounded and killed to a man.

The Persians definitely didn't have elephants, though. Or war rhinos. And the Immortals weren't actually disfigured immortal demon ninjas.

The most detailed account of the battle can be found in Herodotus book 7. Herodotus was born around the time the battle was fought; he visited the site, and boasts that he memorised the names of each of the 300 Spartans who died. Due to the prominence of the battle in other sources and in the image the Spartans broadcast of themselves, we can be fairly sure that it went down more or less as Herodotus describes - although there are interesting signs in later historians such as Diodorus of an alternative tradition about how exactly the battle was fought and lost.

"Ancient Black Ops" ... ultra-elite Krypteia

These words have no connection to historical reality whatsoever.