The film boasted an impressive group of actors from around the world, a script written by Gore Vidal, and experienced, award-winning personnel working behind the camera, alongside a substantial budget. It seems like it should have been great, right? What went wrong here? CALIGULA (1979) possessed so much promise. I often wonder if there’s another reality where Vidal's original, more intense screenplay had ended up with someone like Stanley Kubrick. That version could have given us a SPARTACUS (1960) for a later era. What we actually received is something akin to CENTURIANS OF ROME (1981), but with just as much cocaine involved. Producer Bob Guccione could have justified the expense, the star power, and the studio’s willingness to make an X-rated film – something that hadn't really been done in a significant way since the early 1970s. However, by demanding that his vision include pornography, he missed the mark artistically 𝘢𝘯𝘥 as pornography: It doesn't offer enough intellectual stimulation for those interested in art, and it’s not physically stimulating enough for those with other interests. Despite all this, the film remains a unique oddity. Its continued notoriety allows it to be re-released on different home video formats periodically, attracting viewers—and more importantly, revenue—in a way that resembles a carnival barker drawing people in to see a sideshow attraction. Maybe Guccione understood what he was doing after all.

Source on TMDB