For a lavish Jerry Bruckheimer production that claims to get at the dirty truth behind the legend of Arthur and the knights of the Round Table, King Arthur strains credulity at every turn. When Lancelot (Ioan Gruffudd) asks Guinevere (Keira Knightley, face painted like Madonna on her Vogue tour) if she’s frightened by an army of marauding men, she quips, “Don’t worry, I won’t let them rape you.” That’s the fifth century you don’t get in the history books. Clive Owen does make a stalwart Arthur, fighting for his ideals and a night in bed with Guiney, who gives him fortune-cookie wisdom (“What tomorrow brings we cannot know”). Director Antoine Fuqua seems to have told the actors to “cowboy the fuck up” — a line from his Bruce Willis movie Tears of the Sun. There is one tense battle on ice — the film’s fleeting wisp of glory. The rest is Gladiator lite.