In his memoirs, "Dear Me" (1981), Peter Ustinov recalled that MGM had sought him for the role of Emperor 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 Emperor Nero died when he was thirty, 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." Coincidentally (or not), Ustinov was 30 years old when this movie was released.
Sophia Loren (age 15 when the film was made in 1950) has an uncredited, but easily spotted, bit part as a voluptuous woman who enticingly strews flower petals in the path of Marcus Vinicius' (Robert Taylor's) chariot during the triumphal march. While not her first movie, it was her first American movie, although it was shot in Italy.
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 production chief Louis B. Mayer, an archconservative, unhappy with the script, which used Emperor 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.
Marcus is shown taking his bath in a fairly accurate way. Romans did not have soap - a thing that, along with towels, would not be introduced to Europe until the arrival of Islam. Instead of soap, they would pour oil over the skin and then use a curved tool known as a strigil to scrape of the oil and dirt. If the strigil had a slight edge, it would also lightly scrape the skin, which removed old skin cells and prompted a stimulating flush of blood flow.
The movie's huge box-office success was credited with saving MGM from bankruptcy.