A nachronisms rule in this loud and likable teen romance set in medieval times. Celebrants at an elegant 14th-century ball break into wild, modern abandon to the strains of David Bowie’s “Golden Years.” Budding knights hone their tournament skills accompanied by War’s “Low Rider.” And when they joust, it’s to Queen’s baseline anthem “We Will Rock You.”

Now, if you like your medieval tales all Chaucer-perfect, full of prithee this and demure damsels hidden away in towers, “A Knight’s Tale” will feel like a prolonged, silly action flick that shamelessly panders to the youth market. But, if you embrace pop culture as a contempo hint of modern anthropology, then writer-director Brian Helgeland’s deliberate anachronisms will keep you highly entertained. Think of the movie as if you were spending two hours in Busch Gardens’ “Camelot,” where you know nothing is genuine, but you still have fun.

While purists will argue over the historical sanctity of mixing modern behaviors with medieval characters, there’s no disputing that “A Knight’s Tale” is a star-making vehicle for Heath Ledger. In three steps, Ledger has gone from unknown bad boy in the teeny-bopper romance “10 Things I Hate About You,” to Mel Gibson’s valiant son in “The Patriot,” to star of this swashbuckling romance.

Ledger plays commoner William Thatcher, who’s footloose in France, masquerading as a high-born noble so he can compete in jousting tournaments. He’s accompanied by a ragtag array of boon companions who enjoy watching the talented William pull the wool over the nobles.

Helping to hide William’s lowborn identity are the ever-faithful Roland (“The Full Monty’s” Mark Addy); a viper-tongued blacksmith named Kate (Laura Fraser); the hot-tempered Wat (Alan Tudyk); and, the re-imagined but real historical figure of Chaucer (Paul Bettany). Of course, to keep the youthful crowd engrossed — especially their dates — no self-serving knight’s tale would be complete without a lady to woo and a nefarious villain to best. In this case, Ledger has set his cap for the Lady Jocelyn (spunky newcomer Shannyn Sossamon) while he lives to give the cruel Count Adhemar (Rufus Sewell) his joust desserts.

Taking a page from “Gladiator,” Helgeland tries to fuel the same imaginative flare by once again applying a modern-day sports mentality to an ancient game. Perhaps he should have thought a little harder, because there’s not much one can do to enliven the sport of jousting. Really, it’s just two armored guys on horses charging at each other with wooden lances. One of the more incredible aspects of “A Knight’s Tale” is that cinematographer Richard Greatrex and editor Kevin Stitt find so many ways and angles to spice up the inherently repetitive images. Helgeland fares much better with the script, cleverly making sure each key character has a juicy moment to put on his or her audition reel.

But “A Knight’s Tale” is all about Ledger. With his abundant blond locks tousled to a fare-thee-well, Ledger’s hero is exactly what Helgeland and numerous marketing strategists had their bottom lines set on — a mixed metaphor of manliness, that’s part medieval jouster and part latter-day rock star.

While Helgeland and company do take a stab at poignancy late in the movie, with William finding his long-lost and blind father and struggling with knowing what he’ll lose once he admits his heritage, it’s really too little too late.

If you buy into Helgeland’s time-warped vision of the 14th century, his flagrant incongruities — watching the rabble at a tournament doing the “wave” — “A Knight’s Tale” will be funny and charming. But viewers who don’t sign on to Helgeland’s cheeky conceit from the first strains of “The Boys Are Back in Town,” well, they’ll be gritting their teeth for the next two hours.