Errors made by characters (possibly deliberate errors by the filmmakers): During the scene of the Spartans moving out, they sing "I will Survive". Sonio is clearly seen singing alone, it isn't audible, but you can see his lips singing the song before the music or anyone else is singing.
Continuity: In the scene where Leonidas asks Queen Margo to marry him by writing "Marry Me" on her chest with a sharpie pen, the camera changes positions a couple times during the scene and you can see the words magically disappear each time the camera switches to the wider shot.
Continuity: When Xerxes threatens to write Sparta out of the history books, Leonidas replies: "Well that's fine by me, Xerxes, because I can't read." Previously, he had read the name tattoos on Queen Margo's back, some of them out loud.
Continuity: When the Spartans stop to "replenish" their electrolytes, Sonio is tossed a bottle of "red" Gatorade. However, when they pan back to him after showing a couple of the other warriors, the Gatorade in Sonio's bottle is now "blue".
Revealing mistakes: In the scene where Queen Margo (played by Carmen Electra) flips over for her message, white tape is clearly visible on her breasts.