Based on Frank Miller's graphic novel, "300" is very loosely based the 480 B.C. Battle of Thermopylae, where the King of Sparta led his army against the advancing Persians; the battle is said to have inspired all of Greece to band together against the Persians, and helped usher in the world's first democracy.
This movie contains 22 potentially triggering events.
The oracle scene has underwater-like movements but doesn't technically take place underwater. There is however an underwater shot during the storm with all the ships etc.
The film is about white Greeks fighting brutal, dehumanized Persians, many of which are African. Particularly problematic given the film has been interpreted as an allegory for the wars in Iraq and Afghanistan.
A child dies in the arms of Leonidas and his corpse is carried around for a bit. The skeletons of several babies are shown (though none are killed on screen) and an adult son is decapitated in front of his father.
The film opens with a statement that sickly or disabled babies are left on a mountaintop to die, their skulls are then shown. Later a physically disabled man is initially assumed to be a monster and is called this.
The main antagonist is shown with a lot of facial peircings and is wearing traditional Egyptian makeup. There are several jokes about his appearance throughout the film
While the film does end on a hopeful note, with the Greeks rallied together against the Persians, this is caused by the sacrifice of the 300 with only the narrator surviving to lead the Greeks into battle.
There is a great deal of violence and blood, along with several scenes of decapitation. There are also a great many corpses, which are used to build things several times in the film.