James Mason and Alec Guinness the orators
Whenever they speak in this film they are the voice of reason, but unlike the Stephen Boyd character, Livius, you can buy what they are saying. They make sense but you almost want Livius to just do what Commodus says. Commodus' real father (in the film) was more memorable for me than Stephen Boyd, who just did the whole handsome American for the whole film.
"You're going to cross Sinai?"
"Moses did"