The makers of “Pompeii” might not know much about history or volcanology, but they appear to be well versed in the conventions of Hollywood romantic melodrama. Their movie might be set on land rather than a doomed ocean liner, but it basically recycles the plot of “Titanic,” with Mount Vesuvius taking the place of the killer glacier. It can hardly be said that the romance between youngsters from two different worlds is in quite the same league as the one Leonardo DiCaprio and Kate Winslet shared. The CGI effects are fun to watch, though, especially in the IMAX 3D format. And so while the picture might be a pleasure only in the guiltiest of senses, if you’re willing to leave your brain in the lobby it can be giddily amusing as an exercise in wretched excess.

The hero is Milo (Kit Harrington), whom we first meet as a little boy in northern Britain played by Dylan Schombing, who in 62 A.D. witnesses the entire Celtic tribe to which he belongs—master horsemen, we’re told—massacred by nasty Roman senator Corvus (Kiefer Sutherland, whose nose perhaps inspired the name of his character, which can mean a beak) and his icily murderous lieutenant Proculus (Sasha Roiz). Seventeen years later, Milo has become the most fearsome gladiator in the provincial capital of Londinium, dispatching a quartet of opponents with little more than a couple of knives, a stare of steely determination, and a beautifully sculptured hairdo.

Milo’s talent for mayhem catches the eye of Pompeii’s leading sports impresario Graecus (Joe Pingue), who hustles him off home for a career there. While trudging down the length of Italy to his new home, Milo shows that his family’s skill at horse-whispering has been passed down to him by mercifully killing an animal that’s gone lame while carrying a litter transporting lovely Roman aristocrat Cassia (Emily Browning). Cassia, who’s returning disgusted to Pompeii after a stay in decadent Rome (and, as it happens, is a horse-lover herself, with a favorite steed awaiting her at home), feels the wounded sensitivity in the handsome boy’s soul, and the two share longing glances that signal their love-at-first-sight.

In Pompeii the picture enters a modified “Spartacus” phase, with Milo earning grudging admiration from the resident champ of the arena, Atticus (Adewale Akinnuoye-Agbaje), a noble Nubian who’s one win away from being granted his freedom—something the gladiators’ brutal trainer Bellator (Currie Graham) aims to prevent. And who should arrive for the imminent festival of bloodshed but Senator Corvus, still accompanied by malevolent Proculus, as an emissary of Emperor Titus. (Curiously, the script suggests that Titus has allowed a culture of corruption to flourish in Rome, though historians of the day actually portrayed him as a paragon of a ruler.) Corvus has come south to consider investing in a massive urban redevelopment plan for Pompeii proposed by Cassia’s father Severus (Jared Harris). But it turns out that his throwing money into the venture is contingent on being given the hand of Cassia—something that both the girl and her mother Aurelia (Carrie-Anne Moss) find a revolting idea.

Happily—and unhappily—nature intervenes to undermine the marital negotiations. Vesuvius has been burping and belching, even occasionally swallowing up people like Cassia’s horse steward Felix (Dalmar Abuzeid). (The mount’s occasional outbursts play a role in these early reels not unlike the one Bruce the Shark’s fin had in “Jaws,” presaging the horrors to come.) And after a splashy arena sequence in which Milo and Atticus join forces to annihilate a bunch of gladiators dressed up as Roman legionaries who were supposed to kill them in remembrance of Corvus’ victory over the Celts, all heck breaks loose as Vesuvius erupts, bringing disaster to the city. In the ensuing pandemonium climax piles up upon climax. But among the more important ones Milo must rescue Cassia from the crumbling seaside villa in which she’s been imprisoned, Atticus will have to face off against Proculus, and Milo will of course do battle with Corvus to save his woman and avenge his family honor.

All of this is the sheerest goofiness, marked by stilted acting and laughably banal dialogue courtesy of hack director Paul W.S. Anderson, who most recently delivered the overstuffed bastardization of “The Three Musketeers” featuring his wife Milla Jovovich (also the star of his “Resident Evil” franchise). And while the pure camp level isn’t quite high enough to elevate it to the so-bad-it’s good category, the forty or so minutes of eye-popping, super-destructive visuals that close the movie are undeniably fun to watch especially since they’re riddled with so many moments of juvenile heroics (as when Atticus pauses to rescue an endangered child) and others of villains getting their just deserts. Though you’re hardly going to appreciate the performances of glowering Harington, vacuous Browning, or even sneering Sutherland (Akinnuoye-Agbaje comes off best), it’s difficult to resist the contributions of the behind-the-scenes crew—production designer Paul Denham Austerberry and costume designer Wendy Partridge, but especially the visual effects unit supervised by Dennis Berardi.

The upshot is that while “Pompeii” is by no stretch of the imagination a good movie, if you’re in the right frame of mind it can provide a couple of hours of brainless amusement.