In offering us a grittier, de-mythicized account of Arthur, Guinevere and that knightly third wheel, Lancelot, "King Arthur" director Antoine Fuqua does something funny: He swaps out the old Round Table myths for an even hoarier set of Hollywood stereotypes.

In Fuqua’s alternate version of the Camelot legend, Arthur isn’t a king but an idealistic half-Roman, half-Briton general stationed in the British Isles during the waning days of the Roman Empire. Played with flinty, narrow-shouldered reserve by Clive Owen ("Croupier"), Arthur has spent 15 years pacifying the natives alongside his loyal Summation Knights, a hearty group of Roman conscripts eager to fulfill their army obligations and return home.

One of these knights is Lancelot, played by Welsh actor Ioan Gruffudd ("Wilde") as a handsome deep thinker who amuses himself by cracking jokes about seducing other men’s wives. Contrary to what you might expect, Lancelot’s singular sense of humor never manifests itself as any sort of love triangle. Barring one heart-to-heart moment in the early going, neither do Arthur and Lancelot seem particularly close as comrades, a departure from tradition that drags on the narrative — and our capacity to care about these characters — like a split hoof.

Poised for retirement, Arthur and his men run afoul of that moldiest of action movie cliches, the One Last Job. At the behest of the Pope himself, Arthur must lead his men across Hadrian’s Wall into the untamed north to rescue a prominent Roman family before the settlers fall under the sword of the invading Saxons, led by a pitiless proto-fascist brute named Cerdic (Stellan Skarsgard of "Ronin").

It’s a simple rescue operation until Arthur, in a fit of conscience, decides to lead the Roman governor’s many malnourished slaves to safety, too. Fuqua gets no originality points here — it’s precisely the same heroic dilemma confronted by Bruce Willis in Fuqua’s "Tears of the Sun" (2003). The conceit worked debatably in that movie; here, it reeks strongly of artifice, less debatably.

Along the way, Arthur falls under the spell of Guinevere ("Pirates of the Caribbean: The Curse of the Black Pearl" lassie Keira Knightley), a pagan slave girl he finds teetering near death in a Roman torture chamber. Through Guinevere, Arthur forms an uneasy alliance with Merlin (Stephen Dillane from "The Hours"), the mysterious forest-dwelling mystic who fought Arthur for years as the leader of the island’s native resistance. A motley bunch, the rebels. Long-haired to the last man, smeared in face paint, they appear to have been recruited from Alice Cooper’s touring band.

Inevitably, Arthur gets in touch with his inner Briton and swears to defend the island against the Saxons, forcing his knights to face a shopworn dilemma of their own: Take the easy road out, or stay and fight. Of course, it’s all foreplay for a big, Valhallaian battle scene, but one that is so tamed and bloodless — and stripped of anticipation — that it glances off the audience as harmlessly as a rubber-tipped arrow. Dainty Knightley looks absurd as a snarling battlefield killer, dressed in something so hideous and militantly sexual it could only have been designed by a German.

As mythologist Geoffrey Ashe demonstrated in his book "The Discovery of King Arthur," there is some historical basis for Arthurian legend, but Fuqua ("Training Day") and screenwriter David Franzoni ("Amistad") pursue it at the expense of the grandeur and elegance that characterizes all the best Arthur movies, most particularly John Boorman’s "Excalibur" (1981). Their idea of realism is to have one of Arthur’s knights boast about the size of his genitals, using a very modern-sounding metaphor. During such scenes, one can almost sense the silent, insidious hand of producer Jerry Bruckheimer ("Top Gun").

The actors don’t hold up their end of the Round Table, either. As the fifth-century Saxon villain, Skarsgard talks like he just stumbled out of a 19th-century Kentucky roadhouse, and Owen — whose dark, enigmatic quality worked so well in "Croupier" — is far too remote and bottled up as Arthur.

Funny how "smoldering" becomes "stiff" when you feed it some bad dialogue and stick it on a horse.