In the long-gestating, career-encompassing allegory that is “Megalopolis,” director Francis Ford Coppola puts his name above the title and, in the film’s lone act of modesty, the words “A Fable” beneath it. To call this garish, idea-bloated monstrosity a mere “fable” is to grossly undersell the project’s expansive insights into art, life and legacy. Here, backed by an estimated $120 million of the “Godfather” director’s own money, is the sort of big swing audiences and critics have come to adore him for: a recklessly ambitious, ginormous epic in which humanity’s eternal themes — greed, corruption, loyalty and power — threaten to suffocate a more intimate personal crisis. In this case, a conservative politician and a forward-thinking urban designer clash over the future of a city’s future.

It’s Coppola’s fortune, and he can spend it as he likes, but grandiose title aside, it’s not at all clear why “Megalopolis” needed to be made at such a large scale. For the press screening before its Cannes Film Festival premiere, he insisted that it be seen on the town’s only Imax screen. And yet, so much of the film is shot in close-up, it would play just fine on iPhone screens (apart from the bizarre moment a man walks out, faces the screen and reads a few lines into a microphone). The cast is first-rate, pairing hot young stars like Adam Driver and Aubrey Plaza with Coppola veterans Laurence Fishburne and Giancarlo Esposito, though their performances are oddly cartoonish.

Though it’s been three decades since Coppola’s last triumph, Cannes audiences were hoping he might deliver another “Apocalypse Now.” Turns out, world-building — that invaluable tool of 21st-century Hollywood franchises — may not be in his wheelhouse. Strangely enough, animation (rather than vfx-heavy live action) might have been a better way to tell such a story, helping to balance a tone that’s Shakespearean at times (including a recitation of Hamlet’s most famous monologue) and downright campy at others, as when a browless Shia LaBeouf quips, “Revenge tastes best while wearing a dress.” Animation would’ve also given Coppola more control over a setting meant to synthesize modern New York, ancient Rome and the forests of Pandora. But as one character repeats in the film: “When we leap into the unknown, we prove that we are free.”

In some corners of the real world (such as China and Saudi Arabia), leaders have sought to create forward-thinking “smart cities” from scratch. But that’s not how thriving metropolises typically come to exist. Instead, they’re built up and burned down, then they’re rebuilt and improved in fits and starts, dragged into modernity — not without outrage and criticism — by visionary urban developers like Robert Moses (New York) and Georges-Eugène Haussmann (Paris). Men like Cesar Catilina, the fictional city planner single-handedly trying to drag New Rome into the future, whom Driver plays with the wild-eyed, monomaniacal intensity of Howard Roark (the speechifying architect in Ayn Rand’s “The Fountainhead”).

Like such slow-to-evolve population centers, “Megalopolis” is positively awe-inspiring in some places and an absolute eyesore in others, until you pull back and try to take it all in. Only then can you see the unwieldy way old and new concepts crowd next to another, like an art deco skyscraper squeezed between a cathedral and a Starbucks. The film opens with Catilina stepping off an upper ledge of the Chrysler Building, at which point he commands time to stop. And it does. There, hovering 70-odd stories above the streets of New Rome, he takes a page not from Plutarch (who documented the Catilinarian conspiracy that loosely inspired Coppola), but from the Wachowskis. This time-freezing “Matrix” move — which immediately follows a Laurence Fishburne-narrated scene-setter — suggests something far more fantastical than what follows.

“Megalopolis” is not so much a sci-fi movie, as some have reported, as it is a sexless “Caligula,” transposed to New Rome. The city looks like modern-day Manhattan, except that men sport bowl cuts and women wear see-through robes, made either of gauze or an innovative, all-purpose building material called Megalon, discovered by Catilina and central to his scheme to revamp the city. In this, he is opposed by “slumlord”-turned-mayor Franklyn Cicero (Esposito). The two first have it out at a high-concept press conference, where most of the film’s key figures — including Jon Voight as obscenely rich oligarch Hamilton Crassus III and Plaza as manipulative TV personality Wow Platinum — navigate catwalks dangling amid a scale model of the city. Franklyn plans to erect a casino, whereas Catilina wants to create “a perfect school-city for its people, able to grow along with it.”

To make these competing visions more interesting, Coppola introduces Franklyn’s adult daughter, Julia (Nathalie Emmanuel), an overexposed party girl who gets serious after witnessing Catilina “pause” a building demolition. (Coppola hatched the idea for the film decades ago, but abandoned an earlier plan to make it after the 9/11 terrorist attacks.) Much of the film’s iconography and worldview seem frozen in time, just before and after the 2001 tragedy. What might have felt “too soon” for that moment now feels exasperatingly out of step with today’s concerns, despite a handful of references to Donald Trump and the Jan. 6 riots (including an angry mob seen waving a Confederate flag).

Cicero isn’t happy that his daughter has taken Catilina’s side in the redevelopment scheme. And he’s even more annoyed when Julia falls in love with his adversary, whom ex-DA Cicero once prosecuted over the death of his wife, still unsolved. That subplot introduces an element of ambiguity to Catilina’s otherwise heroic-seeming character. As the film goes on, it feels that Coppola has projected himself onto both Cicero (whose first name, Franklyn, stems from “Francis”) and Catilina (the artist-architect whose ambitions recall the director’s costly Zoetrope Studios folly “One From the Heart”). Family matters to the former, as it clearly does to Coppola, while atoning for infidelity and his “bad boy” ways is part of Catilina’s journey. Their power struggle pales compared to HBO’s brilliant “Succession,” though the film digs into what makes such time-stoppers tick. “When we ask these questions, when we have a dialogue about them, that basically is utopia,” says Catilina.

At times, Coppola injects bawdy and outrageous moments into his “fable,” which keeps the often-sentimental tale from becoming too self-important. Plaza and LaBeouf bring a satirical edge to their scenes, which recalls a previous Cannes debacle, “Southland Tales,” in which Richard Kelly cast comic actors and outside-the-box celebrities (like Dwayne Johnson and Justin Timberlake) to heighten the absurdity. By contrast, most of Coppola’s ensemble is composed of “serious” actors, which lends everything a stilted, almost theatrical quality, while angst-meister Driver taps into those deep wells of internal torment he brought to the “Star Wars” movies. When Catilina steps out onto a giant clock face floating high above New Rome, fuming about the obstacles in his way, he looks not unlike the sulky Kylo Ren.

And yet, apart from Megalon (which sounds suspiciously like James Cameron’s laughable “Unobtanium”), the sci-fi elements here aren’t so far from reality. At one point, characters refer to a Soviet satellite dumping radioactive debris on the city, and though Coppola depicts such a shower, no further mention is made of the disaster. Perhaps the budget didn’t allow for it, which may also explain why no screentime is dedicated to the construction of Catilina’s elaborate urban development project — though it certainly seems like Coppola spared no expense. Consider the wedding scene, so different from the one that opens “The Godfather.” This one transforms Madison Square Garden into a decadent Roman arena, swinging between “Ben-Hur”-style chariot races and a Taylor Swift-sounding original song from Grace VanderWaal, “My Pledge.”

So many big-city movies are told from ground level. That was Sidney Lumet’s specialty, whereas Coppola takes us to the tippy top of the city’s tallest building, or else looks out from floating I-beams on the glowing horizon, where it’s magic hour all the time. The man made four masterpieces — “The Godfather,” “The Conversation,” “The Godfather Part II” and “Apocalypse Now” — and then he made a fortune off his vineyards. He’s seen the world from the upper echelons, rubbed his share of elbows, made his share of mistakes. Instead of retiring comfortably with his wealth, Coppola’s opted to bring us this message, which is part mission statement, part mea culpa. “Megalopolis” is anything but lazy, and while so many of the ideas don’t pan out as planned, this is the kind of late-career statement devotees wanted from the maverick, who never lost his faith in cinema. But now that he’s built it, will they come?