Inspired by the demise of the Roman Empire’s Ninth Legion, a legendary unit founded by Julius Caesar and thought to have met a bitter end nearly two centuries later in what is now Scotland, Centurion is less grandiose than Zack Snyder’s 300 but every bit as brutal. If the sight of severed limbs leaves you squeamish, you’ve been warned.

Those seeking a history lesson would be foolish to consult the latest, bloodiest offering from director Neil Marshall, whose past credits include the crudely effective Dog Soldiers (2002) and The Descent (2005), his claustrophobic venture into a subterranean abyss populated by flesh-hungry humanoids.

Centurion takes itself a bit more seriously than those – it’s based on a supposedly true story, after all – but Marshall, who also wrote the screenplay, is less a conventional humorist than one who revels in the absurdity of his goriest fantasies.

Here, the monsters are neither werewolves nor sun-starved cannibals but men and women mired in a thankless conflict, driven to savagery by either a lust for life or for vengeance. Marshall’s sympathies seem to lie with the Romans, whose gregarious leader Virilus, played by The Wire’s Dominic West, is less politician than populist hero, more dedicated to protecting his men than the Empire’s fading aura of invincibility.

Marshall’s Ninth Legion is outmaneuvered by the Picts, a confederation of Celtic warriors bent on stamping out the Roman threat. Quintus (Michael Fassbender), the steely son of a Roman gladiator, decries the natives’ guerrilla tactics as dishonorable, oblivious to the hypocrisy of the complaint, but no matter: When Virilus is slain by a Pict she-devil (Olga Kurylenko), it is Quintus, unfailingly noble to his last breath, who rallies his fellow Romans from behind enemy lines.

What follows is an unrelenting manhunt more reminiscent of Mel Gibson’s Apocalypto than Snyder’s swords-and-sandals cartoon, though Marshall wisely hits the brakes long enough to give his band of scurrying brothers richer, more complicated characterizations. Heroes, like Quintus, emerge, and so too do self-serving snakes, but we come to understand both, because at the end of the day they want the same thing – to escape with their lives.

Whether they deserve to is another story, and Marshall isn’t shy about sending heroes and villains alike to gruesome deaths. For some, that might be the only reason to see Centurion – the visceral thrill of violence, graphically observed.

But Marshall, as much a storyteller as a stager of geek shows, brings enough substance to the mayhem to give it power beyond a few lurid thrills. The movie, as grim as the war it depicts, affords us little reason to smile, but sufficient reason to care.