This movie marks the return of the screenwriting and producing team of Peter Jackson, Philippa Boyens and Fran Walsh to the epic fantasy genre, after having written and produced all the Lord of the Rings and Hobbit movies. (The credited director here is not Jackson but first-timer Christian Rivers, a storyboard artist on all Jackson’s Tolkien movies.)

The movie is such a curious disaster that it makes you want to ask, “What were they thinking?” But, of course, you know what they were thinking: Mortal Engines is based on the first of a quartet of elaborate fantasy novels that might have launched a new film franchise.

That is not going to happen. Instead, Mortal Engines has quickly become a $100-million-plus disaster, perhaps most embarrassing for its trio of authors because it will sink into oblivion having left barely a mark on the history of moviemaking, not rejected by film audiences so much as entirely ignored.

The movie’s premise makes for better previews than for a full movie: In a barren, post-apocalyptic world 1,000 years in the future, cities have escaped geological upheaval by becoming mobile. The story principally concerns London, a giant, cake-layered parade float with St. Paul’s at its pinnacle and a huge mouth in front that “consumes” smaller wheeled cities. It’s like Minus Tirith from LOTR redecorated as Victorian London and hoisted onto tractor treads big enough to crush an ocean liner.

Turns out London is the bad guy, a predator city run by a couple of heartless power addicts, one of whom is played by Hugo Weaving, graduate of the Matrix and Tolkien trilogies who here seems alternately bored and annoyed. Our heroes are the requisite 20-somethings, who ally themselves with a small army of rebels in steampunk flying machines determined to stop London from…

Does it really matter? No. Does it make any sense? Not really. You’re simply supposed to be so overwhelmed by the visual splendor that you don’t think about niceties like food supplies or natural resources or a thousand years of tread maintenance. (Mortal Engines makes all the Mad Max movies seem remarkably grounded in plausibility.)

And visually splendiferous it is: The various New Zealand-based Weta teams of prop-makers and digital effects artists clearly worked for years at full tilt to create this incoherent but dazzling hodgepodge, and bless them for going home with fat paychecks while some naive film financiers lost their shirts.

To return, then, to our trio of Oscar-winners at their laptops, clicking away at this claptrap: My best guess is that they either haven’t any original ideas in which they’re truly confident — Jackson hasn’t directed an original screenplay since the ho-hum The Frighteners in 1996 — or they can’t get financing for their own creations. So, like London in Mortal Engines, they just keep gobbling up other authors’ works like this and The Lovely Bones and King Kong.

Certainly Jackson and friends must feel some obligation to keep the hundreds of employees of the Weta effects industries employed, and so may be reluctant to return to the smaller, weirder films that launched Jackson’s career. If so, Mortal Engines’ mortal failure may show them the error of their ways.

To put it in Mortal Engine terms: The mighty London must be laid low to free its people to align themselves with goodness once again. Sometimes creativity is best fed by defeat.

Grade: D. Rated PG-13. Now playing at AMC Classic, Biltmore Grande and Carolina Cinemark.

(Photos: Universal Pictures)