The solar eclipse that takes place during the crucifixion scene was the real thing, an event for which director Richard Fleischer delayed shooting in order to capture the ethereal nature of the phenomenon.
Anthony Quinn was appearing on Broadway in "Becket" (as King Henry II) when he was approached to appear in this film. Producer Dino De Laurentiis had to buy up his Broadway contract to secure his release from the play - something Quinn was anxious for him to do, as he greatly disliked his co-star, Laurence Olivier. After Quinn had departed, Olivier continued in the play, but took over Quinn's part instead of continuing in the title role.
As a follow up with producer Dino De Laurentiis, Richard Fleischer planned to make the Sacco and Vanzetti story, but it failed to get off the ground. Fleischer sued Dino but they had made up by 1974 when Fleischer directed " Mandingo" for the Italian producer.