Klaus Kinski, despite playing a rare good guy performance, still proved difficult to work with during filming. He ended up locking heads with everyone involved with the film except for Miguel Bose and the animal wranglers.
Vincent Price was the original choice for the part of Boecius before Klaus Kinski was cast.
While the film gained a U.S. theatrical release in the summer of 1986, after its run in Spain the previous year, it took until 1992 for a North American video release to occur.
Burt Lancaster, Charlton Heston, Kirk Douglas and Robert Mitchum were considered for the role of Boecius.
For some reason, the film became regarded as a public domain title in the U.S. years after its release. Floods of VHS and DVD releases have been floating around the market, usually of poor quality.