There are essentially two things you need to know about 300: It's extremely violent, and it's unlike anything you've seen before.
The first point should come as little surprise for a movie about the Greco-Persian Wars, specifically The Battle of Thermopylae in 480 BC. According to history, King Xerxes (yep, the same guy who takes Esther to be queen in the Bible) launched a massive campaign against Greece with an army that most claim to have numbered in the hundreds of thousands—some even say the millions. Many states were easily conquered by Persia's might, and Sparta seemed poised to fall next.
Not if King Leonidas could help it. Sparta was a militaristic state, reputed for its disciplined warriors—the special-ops forces of their time. As the film tells it, nationalistic pride drove Leonidas to refuse Xerxes' demand for submission. However, despite his requests to dispatch the combined Greek army for retaliation, the local priests and their oracle refused, apparently because of a religious festival—Sparta's equivalent to the Sabbath. As Leonidas asks in the film, what must a king do to save the very city whose laws demand he do nothing?
With defiant loyalty to his country and firm convictions bordering on madness, Leonidas rallied together all he could muster: a small detachment of his 300 finest warriors, plus a small army of less experienced Greeks willing to participate. Those odds seem suicidal, yet the fiercely courageous Spartans managed to wipe out wave after wave of stunned Persian soldiers at a strategic mountain pass, with hope that reinforcements might eventually arrive.
The battle was previously depicted in Rudolph Maté's 1962 film The 300 Spartans, but not with this level of graphic detail. ...1