I've written about Spartacus before. I have a few comments as part of this article, which is an introductory piece, that began as a a session in a dayschool for an Open University Roman history course, and then became an article in a fanzine. It's a very introductory piece, and draws heavily upon the works of the more sensible. I've read and taught a lot more on movies and films since I first wrote this back in the early 2000s, and I should really completely rewrite it now, but for now, let it stand as it is.
I think that this derives from the number of people involved in the shaping of the movie. Stanley Kubrick was the director, but he did not have complete control as he would with later movies. Kirk Douglas, as Executive Producer, initiated the project, and in theory was in charge. Dalton Trumbo wrote the screenplay, drawing upon Howard Fast's novel. Fast had been the original screenwriter, and performed rewrites on Trumbo's script. Anthony Mann had been the original director, shot the first ten minutes of the movies, and prepared a shooting script that was used for the movie's first act. Peter Ustinov, Laurence Olivier and Charles Laughton were pressuring Trumbo to improve their parts, and/or writing their own dialogue (the last particularly in the case of Ustinov). And Ed Muhl, the studio head at Universal, had final approval of the script and cut. All these individuals were pulling in different directions - Fast and Trumbo, both left wing authors, nevertheless had slightly different views of Spartacus. Douglas wanted to make him more heroic and develop the romantic side. Muhl was desperately trying to remove any controversy from a movie that was already controversial because of the subject matter (a hero of the Left since the nineteenth century), and the choice of source novel and screenwriter (both Fast and Trumbo had gone to prison for refusing to co-operate with the House Un-American Activities Committee). What results is a somewhat unsatisfactory compromise between all these approaches. And also good evidence that the auteur theory is not wholly applicable to the Hollywood production system, though of course some auteurists have been determined to find a place for Spartacus in Kubrick's overall body of work.
The other thing I noticed was how really really good Laurence Olivier is. He is the movie's villain, but he is not a cardboard villain. He does genuinely seem to believe that what he wants to do is for the good of Rome, and not just for his own ambition. When he talks of the order he will bring to Rome, he almost makes Fascism seem attractive.
There is also one scene I hadn't appreciated properly. Ustinov and Laughton have a scene together, written by Ustinov, where Laughton talks of how they are both corpulent individuals, and that the corpulent are easy-going - the nastiest tyrants are thin. Underlying this scene, however, is the past careers of Ustinov and Laughton. Both had played Nero, Laughton in The Sign of the Cross (1932) and Ustinov in Quo Vadis (1951). And Nero, of course, was both the nastiest of tyrants and corpulent. I'm sure Ustinov had that subtext in mind.