300, the graphic novel was inspired by the movie, "The 300 Spartans" (1962). The graphic novel and two movies are about The Battle of Thermopylae. This was one of the greatest last-stand battles still taught in military history courses. Others include the Battle of Agincourt. But this one is big because 300 spartans took on 10,000 Persians.

Big write-up here but be careful because it will spoil the movie: http://en.wikipedia.org/wiki/BattleofThermopylae