The credits, concluding with Director Sergio Leone, last over ten minutes into the start of the film.
The final duel between Frank and Harmonica is shot almost exactly like the one in Robert Aldrich's The Last Sunset between Rock Hudson and Kirk Douglas, a film that Bernardo Bertolucci was a huge fan of.
The first draft of the script was 436 pages long.
The Flagstone set reportedly cost as much as the entire budget for Leone's Per un pugno di dollari.
The Indian woman who flees from the train station in the opening sequence was actually played by a Hawaiian princess, Luukialuana (Luana) Kalaeloa (aka Luana Strode). She was the wife of actor Woody Strode.
The main selling point to producers for the use of the Techniscope process was the savings in camera negative. But, another advantage was being able derive the 2.35:1 aspect ratio while shooting with spherical lenses which avoided the distortion created by anamorphics during certain camera moves and extreme close-ups (such as those used by Sergio Leone). This film, together with Il buono, il brutto, il cattivo.(also directed by Leone and shot by Tonino Delli Colli) are now considered masterpieces in the use of the Techniscope system.
The McBain house was built of solid logs that remained following production of the Orson Welles' movie Campanadas a medianoche
The original intent for the opening scene was to use music already composed by composer Ennio Morricone. However, the attempted blend didn't seem to fit well. The decision was made to drop Morricone's score from the opening train station sequence and record the ambient sounds relating to the scenes (including the squeaking windmill and individual footsteps) after Morricone experienced a musical performance created by using only the sounds of a metal ladder. This created an exaggerated version of what had come to be known as "spaghetti sound".
The sheriff was originally to be portrayed by Robert Ryan.
This marked the first of the last three films to be fully directed by Sergio Leone. All three of his last films would be edited for U.S. distribution resulting in box office failure in the U.S. although the uncut international versions would be successful in other countries.
When Henry Fonda was trying to decide whether to be in this film, he asked his friend Eli Wallach, who had just made _Il buono, il brutto, il cattivo. (1966) with Sergio Leone, if he should take the part of Frank. Wallach said that he had to do it and told Fonda, "You will have the time of your life." (Similarly, it was Fonda, saying he considered Leone one of the greatest directors he ever worked with, who persuaded 'James Coburn' to take the part of Mallory in the second "Once Upon a Time..." film, Giù la testa.)
Sergio Leone:
[close-up]
in most gun-fight scenes.
Sergio Leone:
[theme]
Jill, Harmonica, Frank, and Cheyenne.