- Cast the Expert: Ursus was played by Buddy Baer (heavyweight boxer) and Rafał Kubacki (Olympic heavyweight judoka) in the 1951 and 2001 versions respectively.
- Dawson Casting: Robert Taylor was forty when he played Vincius, and was only six years younger than the actor playing his uncle Petronius, Leo Genn. Not an improbable age gap, particularly in Imperial Rome, but it still looks odd to modern viewers.
- Dyeing for Your Art: Robert Taylor's chest reportedly had to be shaved for his part because the studio feared its hairiness might be too "sexy" for a Biblical movie. However, both of Taylor's "beefcake" scenes in the movie still show chest hair.
- Uncredited Role:
- What Could Have Been:
- Henryk Sienkiewicz investigated a possibility to write a sequel, set in the times of Julian the Apostate. However, after doing some research on that period, he scrapped the idea as he figured it would have made the story a lot muddier in the moral sense (ie. no clear dichotomy between Christians and Pagans), and he didn't want to drop that on his readers.
- Clark Gable turned down the role of Marcus Vinicius, because he thought the costume would make him look ridiculous.
- Janet Leigh was considered for the role of Lygia.
- Charles Laughton and Orson Welles were considered for Nero.
- Fredric March and Claude Rains were considered for Petronius.
- Marlene Dietrich was considered for Poppea.
- John Huston was the original director, under the supervision of Producer Arthur Hornblow, with a cast headed by Gregory Peck as Marcus and Elizabeth Taylor as Lygia. The studio was dissatisfied with the footage Huston was sending back from Rome, and Louis B. Mayer, an archconservative, unhappy with the script, which used Nero's persecution of the Christians as an allegory for the anti-Communist witch-hunts, to which Hollywood was then being subjected. After a couple of weeks' shooting, MGM shut down the production, ordered a new script written, re-cast the movie, and persuaded Mervyn LeRoy to assume direction of this movie.
- Amongst the many actresses who tried out for a role in this movie was a pre-stardom Audrey Hepburn.
Trivia / Quo Vadis