Caligula is a 1979 film directed by Tinto Brass, with additional scenes filmed by Giancarlo Lui and Penthouse founder Bob Guccione. The film concerns the rise and fall of Roman Emperor Gaius Caesar Germanicus, better known as "Caligula". Caligula was written by Gore Vidal and co-financed by Penthouse magazine, and produced by Guccione and Franco Rossellini. It stars Malcolm McDowell as the Emperor. Caligula remains the only major motion picture to feature eminent film actors (Sir John Gielgud, Peter O'Toole, Malcolm McDowell, Dame Helen Mirren) in a film with graphic and explicit sex.  The tagline of the film reads, "What would you have done if you had been given absolute power of life and death over everybody else in the whole world?" 
The runtime for this print is 2hrs 35min
I mention this fact because the Wikipedia article referenced above indicates there are several versions both extant and conjectural; none of them has that running time; I tagged it 'uncensored' because of the extremely graphic sexual and violent nature of some of this material.