James Mason was not too impressed with the final result. In an interview he said, "When shooting a western in Spain, one should not say to oneself, 'Never mind, no one is going to see it,' because that will be just the film that the Rank Organisation will choose to release in England!".
The trivia item below may give away important plot points.
Two days prior to filming, producer Bernard Gordon had not heard from the movie's villain, James Mason. He finally got Mason on the phone and arranged to meet him at Madrid airport . When Mason arrived, he was virtually unrecognizable, having decided to live an alternative lifestyle more befitting of the early 1970s counterculture. Once he got into costume, though, Gordon found him to be one of the most cooperative actors he had ever worked with.