|Tarzan's Greatest Adventure (1959) [Slade]: Thrown off of a cliff at the end of a struggle with Gordon Scott.
Damn the Defiant! (HMS Defiant) (1962) [Vizard]: Fatally wounded in a battle with the French fleet; he dies shortly afterwards while talking to Alec Guinness. (Thanks to Gordon)
The Fall of the Roman Empire (1964) [Verulus]: Stabbed to death by Christopher Plummer. (Thanks to Brian)
Operation Crossbow (The Great Spy Mission) (1965) [Bamford]: Killed (off-camera) in an explosion when the RAF bombs the underground missile plant. (Thanks to Gordon)
The Poppy Is Also a Flower (The Opium Connection) (1966) [Captain Vanderbilt]: Shot to death by E.G. Marshall during a struggle on a train. (Thanks to Gordon)
Mackenna's Gold (1969) [Older Englishman]: Killed (off-screen) during a battle between the cavalry, Apache warriors, and Omar Sharif's gang of bandits. He's still alive when we last see him standing in the middle of the melee, but it's strongly implied that he's killed.
The Story of David (1976) [King Saul]: Commits suicide (off-screen) by stabbing himself in the chest with a sword; his body is shown afterwards when the Philistines discover him. (Thanks to Gordon)
Masada (1981) [Rubrius Gallus]: Shot in the neck with an arrow while Anthony is talking to Peter O'Toole. (Thanks to Gordon)
Oedipus at Colonus (1984) [Oedipus]: Dies of old age/natural causes. (Thanks to Gordon)
The Endless Game (1990) [Glanville]: Poisoned (off-screen) by George Segal, simulating a heart attack; we learn of his death afterwards when Albert Finney hears the news.