Sophia Loren has an unbilled, but easily spotted, bit part as a slave girl who strews flower petals in the path of Marcus's chariot during the triumphal march. Whilst not her first film, it was her first American film, although it was shot in Italy.
In his memoirs, "Dear Me" (1981), Ustinov recalled that MGM had sought him for the role of Nero, but dithered for months, refusing to commit. During this time he received numerous telegrams from the studio, one of which stated that they were concerned that he might be too young to play the notorious Roman emperor. Ustinov replied that Nero died when he was 30 and that, if they waited much longer, he'd be too old. The studio cabled back: "Historical research has proved you correct. You have the part."
Filmed at sprawling Cinecitta Studios that had been opened by Benito Mussolini in 1924 as part of the dictator's master plan to make Rome the pre-eminent world capital. Mussolini and Hollywood producer Hal Roach later negotiated to form a partnership, R.A.M.,("Roach and Mussolini") Corporation, which was ultimately aborted. This fascist business alliance horrified 1930's studio moguls and ultimately led to Roach defecting from his MGM distribution deal to United Artists in 1937. Filming in post-war Italy offered the studios immense facilities and cheap Italian labor and extras, of which thousands were required. Hollywood would return to Cinecitta often, producing many of its biggest spectacles there, including Helen of Troy (1956), Ben-Hur (1959) and Cleopatra (1963), the latter two dwarfing even _Quo Vadis_ in scale. It would be later utilized by many Italian producers, including Federico Fellini.
True to his reputation as a voluptuary, the real Petronius took a week to kill himself by allowing his wounds to bleed and binding them up again. Reportedly he entertained friends, ate, drank and slept during the week-long ordeal.
John Huston was the original director, under the supervision of producer Arthur Hornblow, of 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 production chief Louis B. Mayer, an arch-conservative, 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, recast the film, and persuaded Mervyn LeRoy to assume direction of the picture.
Miklós Rózsa's used Galba's March that he composed for the conclusion of the movie again in Ben-Hur (1959) as the music for the opening of the chariot-race sequence, and its conclusion (not to be confused with his famous "Parade of the Charioteers," written specifically for Ben-Hur (1959) that immediately precedes the race proper).
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.
One immediate problem 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 under the stands. Director Mervyn LeRoy overcame this problem by having several costumes stuffed with raw meat and strewn around the ground. This made them appear to audiences to be "people", and the raw meat attracted the lions, who "attacked" and devoured them.
The film does not cover the death of Paul, although he is acknowledged to have been martyred in 67 A.D. It is unclear if he died the same day as Peter and there is disagreement whether he was beheaded or crucified. Unlike Peter, Paul was a Roman citizen and by law no citizen could be crucified.
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". "Art for Art's Sake" is the English translation of "Ars Gratia Artis", which is the motto of MGM, the studio that produced and released this film.
The film represented a hollow victory for MGM studio chief Louis B. Mayer, since it turned out to be his final big-budget production. Produced for $7 million, it was MGM's largest grosser since Gone with the Wind (1939), but Mayer was forced out of his job prior to its release.
Cinecitta simply didn't have enough electrical power to cope with the demands of lighting such immense sets, so generators were shipped over from English studios. They even requisitioned a generator from a decommissioned Italian warship.
The property "Quo Vadis" was being developed by producer Arthur Hornblow in the 1940's. A September 7, 1943, news column by Sheilah Graham reported that Hornblow was considering Laraine Day for a key role.
Announcements by the MGM publicity department ranged from: "In making this film, MGM feel privileged to add something of permanent value to the cultural treasure house of mankind" to "Ancient Rome is going to the dogs, Robert Taylor is going to the lions, and Peter Ustinov is going crazy!".