Buddy Baer's character is named "Ursus". "Ursus" is Latin for "bear".
Kathleen Byron was considered for the role of Lygia.
John Huston was originally supposed to direct this film, but walked out following arguments about the script. He was replaced by Mervyn LeRoy.
Sophia Loren has an unbilled bit part as a slave girl. While not her first film, it was her first American film, although it was shot in Italy.
Sophia Loren's mother, Romilda Villani, also got a bit part as a slave girl.
Clark Gable turned down the role of Marcus Vinicius, because he thought the costume would make him look ridiculous.
Stewart Granger actively sought the lead role, but was unwilling to commit to a long term contract with MGM.
Peter Ustinov would later say that director Mervyn LeRoy gave him the perfect insight as to how to play Nero. LeRoy told him, "I see Nero as a guy who plays with himself nights."
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 film. However, both of Taylor's "beefcake" scenes in the movie still show chest hair.
10 handcarved chariots were made specially for the film.
32,000 costumes were used in the film.
Among the many actresses who tried out for a role in the film: a pre-stardom Audrey Hepburn.
Cinecitta simply didn't have enough power to cope with the filming so generators were shipped over from English studios. They even requisitioned a generator from a decommissioned Italian warship.
Film debut of Bud Spencer (Carlo Pedersoli), who plays one of the Emperor's guards.
Filmed at the new Cincecitta Studio in Rome, a long delayed production complex originally conceived by Benito Mussolini and Hal Roach under their proposed R.A.M. ("Roach and Mussolini") Corporation, which was ultimately aborted. This fascist business alliance horrified 1930s' studio moguls and ultimately led to Roach defecting from his MGM distribution deal to United Artists in 1937. This new studio complex offered massive sets and cheap Italian labor. It would be later utilized by many producers, including Federico Fellini.
In An Audience with Peter Ustinov, Ustinov recalled that he had been attached to the role of Nero for over a year before filming began. During this time he received a memo from the producers, informing him that they still wanted him for the part, but were concerned that he was too young. Ustinov replied that Nero died when he was 31; if they waited much longer, he would be too old for the part. He then received a reply, which he said he had kept and treasured. The reply stated: "Historical research has proved you correct."
Nero remarks on the idea of creating an experience in order to gain inspiration, and complains that for his "conflagration", he has not yet seen a burning city. Petronius replies; "A burning city? That would be carrying art for art's sake too far". "Ars Gratia Artis" is of course the motto of the studio that made the film, MGM.
One immediate problem they encountered with the lions was that when they were released from their cages, they found the arena so hot, they'd immediately retreat back into their cages. Director Mervyn LeRoy overcame this problem by having several costumes filled with meat.
Originally cast in 1949 with Elizabeth Taylor as Lygia and Gregory Peck as Marcus Vinicius. But as the production changed hands the following year, the roles were recast with Deborah Kerr and Robert Taylor.