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.
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.
_"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.