The dull thud of the Roman Empire

Poor Colin Firth. He spends most of "The Last Legion" in a state of absolute blah. I'm not arguing that the movie, one of those combat-heavy costume contraptions, should be anything to put a smile on his face. But even when he's staring into Aishwarya Rai's cleavage, as he occasionally does, he looks like he'd rather be home darning a sock. In his defense, he probably could have seen a gorgeous mannequin anywhere.

Firth plays Aurelius, the glorified security guard for young Romulus Augustus (Thomas Sangster), whom the movie casts as a descendant of Julius Caesar and the future ruler of a kingdom-to-be-determined. You see, the Goths have just sacked Rome and run off with Romulus. So Aurelius and his tiny band of brawlers, including Rai as an unreasonably lusty Indian warrior named Mira, head off to rescue him. Fight sequences and even blander expository dialogue ensue. But why? Most people paying to see this movie have done so for the action scenes, and, my, have these been carelessly mounted and edited. One early siege against the Romans features a bunch of anonymous bodies pushing into each other by torchlight. It's hard to care who's who.

"Last Legion" generically enters the rarely explored crevice between the fall of Rome and the enchanted era of King Arthur (everybody here wants the sword that will be Excalibur). The movie rarely feels fresh. Even an absurd cage-match like "300" cared enough to be both rousing and handsome. There's no fun to be had here.

For one thing, too many very good UK actors have shapeless parts. Peter Mullan does get to characteristically ham it up it once or twice. Actually, the fewer scenes an actor has in "Last Legion" the more he tries to eat them. This may explain Firth's indifference. He'd have too much to chew. And Rai's excuse must be dietary. Scene-eating might be fattening, and who needs the carbs? However, she does throw cutlery and flirt with conviction ("Is that all you see me as: a warrior?").

Ben Kingsley, playing Romulus's intellectual guide, paces himself. He's acted in far worse films with far worse hair. And while it'd be a stretch to say he's enjoying himself, he seems to know how to pass the time, keeping whatever resentment he may have to himself.

That no one screened "Last Legion" for critics seems like a carryover from the apparent boredom driving the action. The film is nothing to be ashamed of (especially if you're Kingsley). But it's as if everybody involved knows what the deal is: It's August. We shouldn't be at this movie; we should be stuck at the airport or off buying school supplies.

Wesley Morris can be reached at wmorris@globe.com. For more on movies, go to boston.com/movie nation.