The movie 300 should definitely not be taken as historical fact. Firstly, it was based off a comic book written by a man known for his over the top characters and stories. Second, the book and film both embrace a longer tradition of Greco-Roman storytelling which involves monsters and the supernatural. These concepts were then twisted and tied to create a modern interpretation of those mythological stories. Third, and most importantly, 300's depiction of the Persian army is extremely problematic. In the movie, the Persians are portrayed as a motley collection of freaks and monsters led by a bizarre and vaguely effeminate king. However, in reality the Persian armies were led by men, whom you would likely recognize. Surely there were those with reputations as monsters, who fought viciously, and who may have been disfigured in previous battles. But these never reached the level of inhumanity portrayed in 300. The Persian army of the actual battle would have more closely resembled today's militaries than that of the film.