The entire film was shot without sound, with the actors looping their lines in post-production.
Bruce Lee dubbed almost all of the English speaking characters in this film including one line for the boss. That line is: "Take him out, but be careful with that gun in public".
According to the assistant director, Ching-Shun Mao, filming around the Colosseum was strictly forbidden, and the few scenes actually filmed there were quickly shot without the knowledge of the Roman authorities.
According to the Bruce Lee documentary, this is Linda Lee Cadwell's (Bruce's wife) favorite of all her husband's films.
Bruce Lee spent forty-five hours on the fight scene with Chuck Norris. His choreographed instructions for the scene took up nearly a quarter of the script.