Historically, the movie was pretty close, although it doesn't show the fact that Athens deployed it's Navy to destroy Xerxes' Navy, the 300 Spartans and 700 Thespians who defended the pass did kill close to a quarter of Xerxes' Army. That demoralizing factor was most important in the later battles when after just 1000 soldiers destroying some 25,000 the Persian forces were a bit reluctant to continue the warm having to face more Spartans in Platea. The movie, although over dramatized for ratings, was good in it's direction and graphics, did have some historical value. The battle really happened, they were betrayed, and had they not been, would have held the pass a lot longer and killed more Persians in doing so.