Robert Ryan's incessant complaints about not receiving top billing so annoyed director Sam Peckinpah that he decided to "punish" Ryan. In the opening credits, after freezing the screen on closeups of William Holden's and Ernest Borgnine's faces while listing them, Peckinpah froze the scene on several horses' rear ends as Ryan was listed.
In an interview, Ben Johnson said that the Mexican women who "frolicked" with him and Warren Oates in the huge wine vats weren't actresses but prostitutes from a nearby brothel, who were hired by Sam Peckinpah so he could tell people that Warner Bros. paid for hookers for his cast.
According to editor Lou Lombardo the original release print contains some 3,643 editorial cuts, more than any other Technicolor film ever processed. Some of these cuts are near subliminal, consisting of three or four frames, making them almost imperceptible to the naked eye.
The train robbery itself was not in the script. All scenes were improvised on the spot, the same day. Same thing with "the walk" for the bunch to help "Angel".
After filming the scene where Ernest Borgnine and William Holden sit by a campfire and their characters vow they "wouldn't have it any other way", it was hard for director Sam Peckinpah to yell, "Cut!" because he was crying.