I remember seeing Charlton Heston on stage during his peak performance in "Man For All Seasons," and he was quite good then. Here, though, which was filmed much earlier, you can see him still developing as an actor. He plays Mark Antony, and the rest of what is described as a well-regarded cast generally follow Shakespeare's account of Caesar’s ascent and decline. Sir John Gielgud takes on that role, and he’s the only truly seasoned performer in this rather unusual group, who deliver some of English literature’s most celebrated lines with differing levels of success. Jason Robards does a respectable job as Brutus, and Diana Rigg (Portia) is also good, but Richard Chamberlain (Octavius), Robert Vaughn (Casca), and Richard Johnson (Cassius) really don't quite measure up, overdoing the language and gestures. The costumes and cinematography are acceptable, yet somehow that contributes to this film’s shortcomings—it doesn’t have the same feeling of immediacy or closeness as a stage production. I actually find myself wondering if the same actors performing this play in a theater might have made it more impressive. It's definitely worth watching; Michael J. Lewis provides a suitably stirring musical score, but ultimately, I don’t believe the final result lives up to its potential.

Source on TMDB