Oscar winner Dame Helen Mirren described the Caligula as “an irresistible mix of art and genitals.”
But the Roman romp, released 45 years ago this month, caused widespread outrage and was instantly banned in most countries.
Littered with full frontal nudity, gruesome , necrophilia and steamy orgy scenes, the movie is enjoying a new audience after it was rereleased this week with never-before-seen footage.
Dame Helen, 79, who stars as the Emperor’s notoriously promiscuous wife Caesonia, has dismissed controversy but admits that "everyone was naked" on set.
But Penthouse models later claimed they were forced into performing genuine sex acts in orgy scenes by their seedy boss, who produced the film.
It remains mired in controversy even now.
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The new version has been repurposed and reimagined by American historian Thomas Negovan, who unearthed more than 90 hours of previously unseen footage from the famously chaotic shoot in Rome.
He has chosen different angles so the shots appear less exploitative and some of the hardcore sex has been removed.
Caligula: The Ultimate Cut, which is over three hours long, may be less lurid than the original, but there are still is still plenty of sexual violence in the film, which also stars Malcolm McDowell and Sir John Gielgud.
In one particularly shocking scene, Caligula rapes both a bride and groom at their wedding.
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He visits a brothel in Rome, where permanently orgasming women splash in a pool while they wait to be chosen for “ravishment” by Caesar.
In other debauched scenes, Caligula sexually abuses a male courtier, and has sex with his dead sister.
He sends handsome men to their deaths while ordering beautiful women to strip naked and submit to his urges.
At least a gruesome castration scene has been, erm, cut.
In real life, the Emperor was so depraved he slept with all three of his sisters, wanted to marry his horse and was so touchy about his bald spot that if he caught anyone looking down on it, he sentenced them to death.
In the film Mirren’s character gives birth spread-eagled and suspended in front of the Imperial court.
She said: "I was doing nude scenes from the moment I first started doing movies.
“I never wanted to show much boobs, but I thought, ‘Does it really matter?’ It seemed to be nothing to get your knickers in a twist over."
She added: "Everyone was naked in that. It was like showing up for a nudist camp every day. You felt embarrassed if you had your clothes on in that movie."
In a career spanning six decades, she has stripped in films from 1969's Age of Consent to 2003's Calendar Girls.
And eye-popping scenes in iconic movies like Excalibur and Cal have cemented her position as a sex symbol.
But the star admits times have changed: “When I was doing Caligula, it was 'shock, horror, XX. Only in porn cinemas.
"But now, with Game of Thrones, it's on at 8pm and everything's a sex scene."
"Everyone was naked in that. It was like showing up for a nudist camp every day. You felt embarrassed if you had your clothes on in that movie."
Helen Mirren
She only appeared for nine minutes in the original film, but she’s in the new version for over an hour.
'Absolutely horrifying'
Caligula was the first-ever production by Penthouse Films International, part of the erotic magazine empire owned by notorious porn baron Bob Guccione.
At the time he was locked in a bitter war with Playboy publisher Hugh Hefner, their rivalry became known as the Pubic Wars.
Hefner had not succeeded in the film business so Guccione, determined to break new ground, insisted on copious nudity from the start.
At the time it was the most expensive movie ever produced - with 3592 costumes and 2000 wigs were made, along with a 175ft long Roman galley. Unfortunately it leaked.
Mirren was paid £40,000, which she spent on her first house and acres of forest in Scotland.
Co-star Sir John Gielgud, whose character Nerva kills himself twenty minutes into the film, was delighted to be surrounded by dozens of naked men on set.
He said later: “The moment the bell rang for lunch, they all put their hands in front of their genitals and rushed off to have a pizza with their families.”
Even after filming wrapped in Rome in 1976, Guccione secretly shot extra pornographic scenes - and spliced the hardcore material into the final cut.
He did not tell writer Gore Vidal or director and “erotic genre” specialist Tinto Brass, who were horrified by Guccione’s post-production betrayal.
They argued that the scenes had been added for titillation value alone.
In an interview with Conan O'Brien, Malcolm spoke about how the porn scenes shot after the movie didn't match what was initially captured on camera.
"It didn't even fit because the photography was all grainy - a completely different photography", he said. "You could see that it didn't match.
"Nothing matched. But it didn't matter. It still made over $100million, they say. I'm still waiting for my cheque, Bob."
He also spoke about how amazed John Gielgud was about all the frontal nudity in the film.
"I said to him, how come Sir John, a knight of the realm, is in a porno movie. [He said] 'Oh, I don't think so. It's rather a good film, isn't it? I've just come from the set. Have you seen all that c***? I haven't seen so much c*** in my life.'"
'Real' orgy
British model Jane Hargrave was one of the girls Guccione recruited for the additional scenes featuring ‘Imperial Brothel Workers.’
She had become a Penthouse 'Pet' after applying to an ad she read while sitting her A Levels at a Catholic school - and meeting Bob Guccione.
“He had quite a presence. He had a lot of power and this very deep God's voice," she says.
“He said that he needed to have a look at me. I have to go upstairs into the bathroom, take my clothes off and he's sitting in the bedroom.
“I stood there naked. I just had to overcome my shyness."
But two weeks later Jane flew to New York, then to a private island near Honduras for a shoot, where she and Guccione “developed a friendship”.
She added: “He asked if I would mind if he trimmed my pubic hair.”
By this time the millionaire was living in a 42-room New York townhouse with new partner Kathy Keeton, an executive at the company.
Jane moved into the couple’s dressing room - linked to their bedroom through an adjoining shower - and Guccione would come to her bed while Kathy slept next door.
It emerged that he recruited dozens of models, known as Pets, who were cajoled into orgies, fed contraceptive pills to make their breasts bigger and forced to watch bestiality videos.
“When Kathy was away he asked me into the master bedroom,” said Jane.
“He had a video of women having sex with animals. A girl with a pig. I think he wanted to shock me.”
But she finally realised how exploitative he was after he cajoled the Pets into appearing in the movie, with Jane playing the Priestess of Isis.
They were expected to engage in real sex acts.
“He wanted us all to take part in an orgy. I was literally still a teenager,” she said, adding that she had not even been intimate with a man before meeting Guccione.
She realised “how unimportant I was to a man we're supposed to trust” and left.
Guccione’s daughter Nina also recalled being forced to go to a screening of Caligula at the age of 18 and found it "absolutely horrifying".
He had a video of women having sex with animals. A girl with a pig. I think he wanted to shock me.
Jane Hargrave
"I'd never seen a sex film. I was speechless and very upset," she said.
"No good parent should expose their child to that. But being a narcissist, he had no empathy.”
Caligula Controversy
Caligula was released in 1979 and original screenwriter Gore Vidal and film director Tinto Brass petitioned to have their names taken off the credits after more extreme material was added.
Producer Bob Guccione, founder of Penthouse magazine, engaged Giancarlo Lui to film post-production scenes featuring hardcore sex, without Brass’s consent.
Initially released to Italian cinemas then in America the following year, Caligula was met with legal issues and controversies over its violent and sexual content and was banned in numerous countries, but it has since become a cult classic.
Caligula: The Ultimate Cut is in selected cinemas now.
But the film flopped and was panned by critics, costing Guccione millions. Leading man Malcolm McDowell was so ashamed he emigrated.
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“It wasn’t supposed to be a porn movie,” says Negovan. "You think Helen Mirren and John Gielgud took a job in a porn movie with no plot?
“No, that’s the point. Like it had a script. It had incredible sets, incredible costumes. And people really sweated to make this film.”