It's King Arthur, Jim, but not as we know it. Shot in Co Wicklow where the legend began - you've seen Excalibur - the latest celluloid spin on Arthurian legend is being marketed in the US as being ' based on a true story'. Hugh Linehan went to LA - the perfect venue to introduce a movie set in the Dark Ages - to talk to the cast and crew

Chivalry is dead, apparently. The latest spin on the venerable cycle of movies based on the story of King Arthur and his Knights of the Round Table gets rid of the hocus-pocus, barely hints at the possibility of hanky-panky between Guinevere and Lancelot and relegates Merlin to a bit-part as a wild man of the woods. Excalibur? Blink and you'll miss it. In the hands of director Antoine Fuqua (Training Day), writer David Franzoni (Gladiator) and producer Jerry Bruckheimer (more blockbusters than would fit on this page), the new King Arthur (shot last summer in the bleakest-looking parts of Co Wicklow) turns its back on Thomas Malory's medieval tales of dashing knights and damsels, setting the story in the Dark Ages, which is where, apparently, it came from in the first place.

In fact, this King Arthur is so far removed from the story as we think we know it that, were it not for the title and the names of some of the characters, you might not recognise it at all. And, given that it's all a bit confusing, it requires sone explanation. So here goes (deep breath). We are in the 5th century. The Roman Empire is declining and falling. In Northern Britain, at Hadrian's wall, a Romano-British commander, Lucius Artorius Castus, commands a troop of indentured soldiers (with names such as Galahad, Lancelot etc) who hail originally from Sarmatia, by the Black Sea and who are in constant conflict with roving guerrilla bands of the local population (known here as Woads, after their blue body-paint, but roughly corresponding to Celts and Picts). As if that weren't bad enough, the whole shebang is threatened by a regiment of monstrous Saxons who have landed north of the Wall, and are raping and pillaging their way in our heroes' direction. Oh, and did I mention that Artorius (or Arthur as he's known to his pals) is a follower of the Pelagian heresy, which holds that men have free will, and also that a slimy Man of the Church has arrived from Rome to tell the troops that, before they're free to return home, they must undertake One Last Deadly Job? In the past, Mel Ferrer. Sean Connery, Nigel Terry, Richard Harris and (this writer's personal favourite) Monty Python's Graham Chapman have all donned the armour and pulled the sword from the stone in movies ranging from the bland to the hilarious to the not-bad-at-all. On the face of it, though, this is the most radical re-working to date.

Sitting in a screening theatre on Hollywood's Wilshire Boulevard for the press preview of King Arthur on a Tuesday evening, we are mildly surprised to be told by Fuqua that some scenes in the film we're about to see were only shot on the previous Saturday. Coming on top of rumours last autumn in Ireland of a production well over schedule and way over budget, it all points to a difficult gestation period for this revisionist swords, sandals, mud and ice epic. Not that this necessarily means anything for the finished product - some of the worst films ever made sailed happily through the production process, and some of the best were nightmarish experiences for all concerned - but it seems to imply that shoehorning all that stuff into a manageable multiplex product has proved a little tricky.

Then there's the issue of the casting - the billboards along Sunset Strip announce the imminent arrival of KA, but the posters are dominated by Keira Knightley's Amazon warrior-queen, Guinevere, rather than Clive Owen as Arthur. Knightley - a hot property after the success of Pirates of the Caribbean - clearly is hotter than Owen, however respected the latter may be for his performances in films such as Croupier and Gosford Park. I am meeting the stars and makers of King Arthur in Los Angeles the week before the film's US release, and already things are looking slightly ominous. The big buzz in Tinseltown is all about Spider-Man, with a lesser but still significant amount of noise around Fahrenheit 9/11. King Arthur, with its lack of big-name stars and rather confusing storyline, seems set for a tougher ride.

Maybe it's something to do with my European sensibilities, but what seems particularly strange about the whole marketing campaign is its insistence that King Arthur, of all things, is now "based on a true story". Historians have been enlisted to back up the thesis that the once and future king was in fact largely based on Artorius. All fine and dandy, and mildly interesting perhaps, but all this "At Last - The Truth!" stuff seems a bit odd when it comes to a subject which by its very nature is essentially mythic and mystical.

"This is only an interpretation," says Clive Owen after we've seen the film. "I would never stand up and say this is the real or the definitive story. But it's based on an historical context, that has been researched. And it's as valid as any other version of the story, or even more so, because of that. I was surprised. I didn't know that much about King Arthur. For me it was children's storybooks and movies. Then I discovered that the myth had changed and developed over many hundreds of years. But the stories have to start somewhere. That's what the film's about."

Surely one of the downsides of that approach, though, is that it takes the magic out of the story. "That's what the film is saying. It brings us up to the start of the mythmaking."

This is the first time Owen has taken the lead role in an action blockbuster. One wonders whether he was surprised to find his character was more complex, or confused, than one would normally expect from the genre. "Well, Arthur's ideals about Rome are challenged," he says. "Rome's changing and he has to change too. It may be more complicated than your usual action character's narrative arc, but it's still pretty straightforward."

Keira Knightley, whose star certainly seems to be in the rapid ascendant, doesn't actually appear until nearly an hour into the film, despite her billing on the posters. "It's a really interesting idea," says Knightley. "That you take these myths and legends and put them in a very grounded place in history. As opposed to Guinevere being this very romantic, innocent vision, we've tried to turn that traditional character on her head and make her a very strong, powerful being. It's a matriarchal society, which makes Guinevere a leader in her own right, who would have fought alongside men. That gives the character more depth. She's fighting for the freedom of her people, almost like a guerrilla fighter."

David Franzoni has a rather earthier take on the issue. The screenwriter, who made his name with the cringe-making Jumping Jack Flash, now seems to have reinvented himself as Hollywood's foremost reviver of the Roman Empire, with Gladiator, King Arthur and the forthcoming Hannibal (the one with the elephants rather than the one with the fava beans) all on his CV. "I don't like the mythical tales of Arthur," says Franzoni. "Guinevere is this Christianised, bored housewife who fucks the poolboy. That's basically Christian mythology - women are rich tramps - and I despise that in our literature and in our culture. And Arthur in the Celtic Christian legends is so passive, so boring. But Lucius Artorius Castus is fascinating,"

For Franzoni, the most interesting element was the depiction of the warlike Sarmatians, pressganged into the service of the declining Empire. "For a long time, historians have noticed that there's a huge correlation between the Arthurian myth and the legends of the Sarmatians," he says. "But they couldn't figure out how they connected with each other. Marcus Aurelius defeated the Sarmatians and sent 5,500 to serve him in Britain. That interested me, and when I was in Rome working on Gladiator I started reading about the Sarmatians. If you read Ovid, he was exiled to the Black Sea by Augustus, where he lived right next to the same tribe that were later sent to Britain. He writes about it, and it was like living next door to the worst Hell's Angels you can ever imagine. The complete opposite of gallant knights. These were completely out of control, fighting, raping, killing." Franzoni's eyes get a gleam in them as he recounts all this, and it's not surprising that he welcomes comparisons with The Wild Bunch, and with the Vietnam War.

"I modelled it after the fall of Saigon," he says. "The last helicopters are leaving, the Special Forces have to do one last mission in the DMZ. They hate what they're doing, they're hated by the people around them. They just want to get home."

For Antoine Fuqua, the reference point was the films of Akira Kurosawa, along with a desire to make an epic movie that wasn't over-reliant on computer-generated imagery. I wonder was it also the opportunity to shoot a real-life bone-crunching historical epic that attracted him to the project. "Yes, and also because I really wanted it to be a character piece. You see so many epic movies. I thought let's personalise it, make it smaller." He didn't anticipate the Irish weather, though. King Arthur was conceived as a dark, wintry tale set against the bleak backdrop of Dark Ages northern Britain. As luck would have it, 2003 was one of those years when Ireland actually had something close to a real summer. What Fuqua couldn't handle was the unpredictability. "It was difficult. I'd be coming out to set in the morning and I'd ask my driver what's the weather going to be like. He'd say 'um, sunny, a bit cloudy, possible rain, possible flooding.' And he was half serious. We're trying to shoot this deep, dark stuff, all of a sudden the sun comes out and people are walking around with their shirts off. Of course by evening you're freezing your butt off again. I hated it for half of the movie, and then I did a couple of shots where I saw the shadows moving over the scenery, and I thought 'Oh, that's great'."

From listening to Franzoni and Fuqua, one gets the impression that there might have been a much darker, twisted and more violent movie in all this material than ended up in the finished version, something Franzoni hints at when I ask him about the rather bland and extremely ahistorical imposition of 21st century values on the story. Very stupid filmgoers may find themselves leaving the cinema labouring under the misapprehension that fifth-century Britons were fighting for universal suffrage, equality between the sexes and a more caring, sharing society.

"It got changed," Franzoni says wearily. "I don't have control over it. In the end, I said OK." Fuqua also sounds as if he now wants to distance himself slightly from the film. It's no secret that he wanted bloodier, nastier battles, but that the studio insisted on a cut which would gain the commercially vital PG-13 rating in the US. Given that the film was still shooting up to a couple of days before we see it, I ask what sort of pressure that puts on a director. "It's the worst place you can be," he says. "You're vulnerable to everything. You're vulnerable to PG-13, because they're going 'You've gotta finish the movie! And by the way, you've got to do a different version.' And you're going 'What are you talking about?' But, you know, you do one film for them and one for you. That's what you gotta do."

And does he really believe that it's a good idea to take all the magic out of the myth? "You don't have to let go of the magic," says Fuqua. "In relation to this particular movie - in today's society there's a lack of heroes. Every culture has great heroes from its past. If you're going to do that you have to ground it, to see if there's some truth in these stories. That's important, because it's time to get away from these cartoon heroes and try to find some truth. Is it more interesting to make a film about the sword or about the man? To me the man is more interesting."

• King Arthur opens on July 30th