 Producer Irwin Allen called Spain "a wonderful country to make pictures in" because of its more than 2,000 old castles, twelve of which were used in the film.Halfway through production, Bryan Forbes was called in to do some rewriting of the script (he is credited as "additional dialogue by...").According to Forbes's memoirs, Alan Ladd's wife and long-time agent, Sue Carol, had script approval and objected to a scene where her husband's character stole a horse.