The film slipped into the public domain not long after its theatrical run was over. That explains why so many poor-quality versions of the film are available.
In his autobiography "The Actor's Life - Journals 1956-1976", Charlton Heston wrote, "We're faced with the endless problems of organization, personnel, dogs, publicity . . . I fear I've fallen in with amateurs and con men. This had not been a picture really but a production deal, patched together with incredible adroitness and negotiating skill--and no filmmaking talent whatsoever."
Charlton Heston didn't enjoy making this film. He found the whole experience completely disorganized from the start. He later named it as his least favorite of all the films he had appeared in.
Charlton Heston had to use real bullets in the scene where he shot at the wolves, shooting over their heads, because the crew forgot to get blanks.
Juan Luis Galiardo had a nervous breakdown while acting in this film and was unable to finish his part. Sancho García replaced him, playing a different character in Galliardo's unfinished scenes.