Clark Gable warned Gary Cooper not to work with Burt Lancaster, saying, "That young guy will blow you off the screen." Ironically, four years later Gable would work with Lancaster in Run Silent Run Deep (1958).
Gary Cooper was badly hurt when he was struck by fragments from a bridge that was blown up during filming because the special effects team used too much explosive.
The film was shot entirely on-location in Mexico. One day during a break in filming, Charles Bronson and Ernest Borgnine decided to go to the nearest town for cigarettes. This meant saddling up in costume, sidearms and all, and riding to town. On the way, the two were spotted by a truck full of federales who, mistaking them for bandits, stopped the pair and held them at gunpoint until representatives from the film company showed up to vouch for them.
In his autobiography, Ernest Borgnine reports that, during the shooting, Burt Lancaster brought his children on the set and all of them laughed at Jack Elam because of his lifeless left eye. Elam, of course, was upset because of this, and he and Lancaster got into a fist fight.
Last time actor Charles Bronson was billed under his real name Charles Buchinsky in a major film.