Montgomery Clift only agreed to do this movie so that he could later do Reflections in a Golden Eye (1967). Following his death, the role went to Marlon Brando.
Clift insisted on doing all of the stunts in this film himself, which he did despite poor health.
This movie's lead cast is completely cosmopolitan: Montgomery Clift is American, Hardy Krüger is German and Roddy McDowall is English whilst the movie was directed by a Belgian, Raoul Lévy.