_"Price is Right, The" (1956)_ gave the role of an extra in this film away as a bonus prize. The winner was a man named Robert Reynolds, and he can be seen in the background of one of the arena scenes.
Alec Guinness admitted that he never saw more than twenty minutes of the completed film.
Sophia Loren's salary for the film was $1,000,000 becoming the second actress (behind Elizabeth Taylor for Cleopatra) to receive that amount for a single film.
Richard Harris was originally cast as Commodus. He withdrew because of artistic differences with the director. He was replaced by Christopher Plummer.
Stephen Boyd blamed the massive commercial failure of The Fall of the Roman Empire for ruining his movie career.
At 1312 by 754 ft., the Roman Forum still holds the record as the largest outdoor set ever built for a film.
Budgeted at about $20 million, this was Paramount's biggest flop of 1964. Its failure cost producer Samuel Bronston his Spanish production facility.
First cinema film of Eric Porter.
The film was originally intended to be made after El Cid and to reunite Charlton Heston and Sophia Loren. The set for the Forum Romanum was actually being built when Heston rejected the script but expressed an interest in '55 Days at Peking' instead. Samuel Bronston immediately ordered that the work on the Forum be stopped and the landscaping and foundation work be adapted for the Peking set. After filming, the Peking set was torn down and replaced by the Forum. If you look carefully, both sets share a very similar topography.