- Adaptation First: The film is actually based on Frank Miller's Xerxes, which wasn't released until April 2018, four years after the movie was released.
- Awesome, Dear Boy: This film fulfilled Eva Green's long-held acting dream of playing an action hero in a movie.
- B-Team Sequel: Zack Snyder produced and wrote it but didn't return to direct, as he was very busy with his work on the DC Extended Universe jumping from the production of Man of Steel to that of Batman v Superman: Dawn of Justice, so he and his wife Deborah (co-producer via Cruel and Unusual Films) entrusted Noam Murro to direct it.
- Dyeing for Your Art: Sullivan Stapleton revealed that this was a role which absolutely required him "to get a six-pack for the first time in my life" and he reportedly adopted a diet of almost 100% yogurt for the duration of the shoot to maintain it.
- What Could Have Been:
- Zack Snyder originally planned to direct it, but he got too busy starting the DC Extended Universe, so he chose Noam Murro to direct instead.
- Gerard Butler was offered the chance to come back as Leonidas but he declined. The first scene between Themistocles and Gorgo definitely feels like it was originally written with Butler's Leonidas in mind.
- Matt Smith turned down the role of Aesyklos.
- The movie was initially going to be about the story of Xerxes and his military expeditions. The story and narrative were changed significantly and the script was revised in subsequent drafts to have the Athenian leader Themistocles included.
- Working Title: The film was previously called Xerxes, the title of the Frank Miller graphic novel on which the film is based, and later 300: The Battle of Artemisia, the title used during filming. Ultimately, the present title was used because the other two were deemed too exotic.
Trivia / 300: Rise of an Empire