I'm not sure if this has been mentioned yet, but I found a rather interesting precursor to 300... a 1962 film named the 300 spartans! I was researching an old favourite show called the Time Tunnel and I noticed some of the film footage used for an episode of the show was from this little-known film on the Battle of Thermopylae.

The 300 Spartans

Quote Originally Posted by the 300 Spartans - Wikipedia entry
The 300 Spartans is a 1962 film depicting the Battle of Thermopylae. Made with the cooperation of the Greek government, it was shot in the village of Perachora in the Peloponnese. The picture was noted for its Cold War overtones, and starred Richard Egan as the Spartan king Leonidas, Ralph Richardson as Themistocles of Athens and David Farrar as Persian king Xerxes, with Diane Baker as Ellas and Barry Coe as Phylon providing the requisite romantic element in the film.

Frank Miller saw this movie as a boy and said it "changed the course of my creative life."[1] His graphic novel 300 is about the Battle of Thermopylae, as is its 2007 film adaptation.
I always suspected most current films were gritty re-hashes of ancient, forgotten foreign films. :rolleyes2