Damien Chazelle has been working on the story for Babylon, at least in his head, ever since he first moved to Los Angeles around 15 years ago. “The basic idea was just to do a big, epic, multicharacter movie, set in these early days of Los Angeles and Hollywood, when both of these things were coming into what we now think of them as,” he tells Vanity Fair in his first interview about the film, which is due out from Paramount this December.

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The 1920s were a pivotal moment in Hollywood history. Los Angeles was transforming into a metropolis, and the movie industry—making the uncertain transition from silent films to the talkies—was bursting with people angling for fame, wealth, and power.

A decade and a half ago, Chazelle had none of those things as an aspiring writer-director who had recently moved to LA. He had not yet had his breakout Sundance debut with Whiplash—which went on to win J.K. Simmons a best-supporting-actor Oscar for his turn as an explosive jazz instructor—nor had he become the youngest person to ever win the best-director Oscar, for La La Land. “I kept putting it off, because it was just a little too massive,” Chazelle says of the project. He finally tackled the screenplay after finishing his 2018 film First Man, with Ryan Gosling as Neil Armstrong.

Based on early footage and images, Babylon looks to be a lavish romp through Hollywood’s nascent Golden Age, starring a brash Brad Pitt, an uninhibited Margot Robbie, and newcomer Diego Calva. But beneath the glitz and glamour, Chazelle wanted Babylon to underscore the fact that the town’s rapid change and growth came at a price. “Everything is shifting underneath people’s feet,” he says, “and I became really fascinated by the human cost of disruption at that magnitude, at a time when there was no road map, when everything was just new and wild.”

Casting two of Hollywood’s biggest movie stars in Babylon’s lead roles made sense thematically, as well as financially. Pitt and Robbie, who starred together in Once Upon a Time…in Hollywood, play actors at very different points in their careers, and Chazelle knew his stars would see echoes of their own lives in the parts. “Part of what was magical about working with them in these roles is that each of them felt like they were really able to make the performance the most personal thing they had done,” he says.

The majority of characters in Babylon are fictional, though Chazelle took inspiration from real-life Hollywood stars. Pitt’s character, Jack Conrad, is a hard-partying “über-movie star,” as Chazelle puts it, inspired by the likes of John Gilbert, Clark Gable, and Douglas Fairbanks: “He’s reaching a point in his life in his career where he’s starting to look back and starting to wonder what’s ahead.” (Pitt expressed a similar sentiment about his own work in a recent GQ cover story.)

As for Robbie, she’s playing Nellie LaRoy, a scrappy aspiring actress who’s an amalgam of early stars like Clara Bow, Jeanne Eagels, Joan Crawford, and Alma Rubens. Nellie is a new Hollywood transplant who’s suddenly in the spotlight, an experience that the Wolf of Wall Street’s breakout could relate to. “Margot as a person has this—it’s a very Australian sort of thing—brash, bold, hungry kind of edge to her that she was really able to tap into and do a lot of really fun things with,” says Chazelle.

Calva, the cast’s newcomer, plays Manny Torres, a Mexican immigrant who, as an outsider in Hollywood, serves as the audience’s eyes in the world of Babylon. Says Chazelle, “In many ways, he was going through a very similar experience to the character he was playing as well, of just stumbling on a larger-than-life campus and going, ‘What the fuck is going on?’”

Babylon’s rich supporting cast—including Jovan Adepo, Li Jun Li, Jean Smart, and Tobey Maguire—also play fictional characters (the only named real-life person in the main ensemble is producer Irving Thalberg, played by Max Minghella), whose dreams of fame and success rest on navigating a perilous town.

Chazelle brought together many of his past collaborators, including cinematographer Linus Sandgren and composer Justin Hurwitz, who both won Oscars for La La Land. He had in mind a movie packed with spectacle that reflected the extravagance and hedonism of the era: “I wanted to capture just how big and bold and brash and unapologetic that world was.”

But Chazelle wanted to plumb the lower depths too—to juxtapose La La Land’s gorgeous, Hollywood-glam set pieces and Whiplash’s darker examination of ambition’s toll. “It was really a wild West period for these people, this gallery of characters, as they rise and fall, rise, fall, rise again, fall again,” he says, adding that “the thing that they’re building is springing back on them and chewing them up.”

Expect a story that explores the multiple levels of transformation, from the city itself to the industry, and the people hoping to make it big. Chazelle references the “headlong, heedless ambition” of that time as a central theme of his movie. And not coincidentally, he says Babylon is his most ambitious work yet: “It was definitely the hardest thing I’ve done. Just the logistics of it, the number of characters, the scale of the set pieces, the span of time that the movie charts—it all conspired to make it particularly challenging, but it was a challenge that was pretty exciting to take on.”

Babylon will be released in theaters on December 25 by Paramount. This feature is part of Awards Insider’s exclusive awards coverage, featuring first looks and in-depth interviews with some of this coming season’s biggest contenders.