The film was originally envisioned and shot as an R-rated film with corresponding graphic violence. However, after the picture had been edited, Disney executives demanded it be changed to a PG-13, hence necessitating a lot of effects work to remove the blood from the battle scenes. Director Antoine Fuqua and producer Jerry Bruckheimer were not at all pleased with this decision and fought against it, but were ultimately overruled. They were both disappointed with the theatrical release and later released a much more violent Director's Cut on DVD. However, according to Fuqua's commentary track, even the Director's Cut version is considerably less violent than his ideal version. Ironically, when the film was released, one of the biggest criticisms was that the battles were mysteriously bloodless, hence undermining any sense of realism.
In an interview with Express Magazine on 24 July 2004, ("Keira Slays The Knights" by John Millar) Keira Knightley disclosed that her breasts were digitally enhanced on the American movie posters to make them appear larger.
According to Ioan Gruffudd (Lancelot), the camera operator wore a motorcycle crash helmet and was constantly surrounded by men with riot shields because of the intense action sequences happening around him.
Stellan Skarsgård played the role of Cerdic as if he was bored with killing and conquering and was simply doing it out of instinct and because he had nothing else better to do; this is why he raises his arms into the air and cheers after meeting Arthur; he has found someone worth getting excited about fighting.
In David Franzoni's original script, the love triangle so central to the original myth between Arthur, Guinevere and Lancelot was a major part of the plot, as it is in most filmic adaptations of the Arthurian legend (such as John Boorman's Excalibur (1981) for example). However, during his research for the film, director Antoine Fuqua came to believe that there was no truth to the love triangle aspect of the story and had Franzoni rewrite the script without it.
After several poor test screenings, the producers became concerned that there wasn't enough humor in the film, and on June 16, thirteen days before the US premiere, the scene in which Bors (Ray Winstone) reveals that his numerous children have numbers instead of names was shot.
All of the principal actors attended a two week boot camp under the supervisor of stunt coordinator Steve Dent. The training included horse-riding, combat riding, archery, boxing, sword fighting, weight training and wilderness social bonding. Because of his age, Ray Winstone didn't attend boot camp, but he had boxed in his youth and this was incorporated into his character.
The Woads in the film are supposed to be Picts. The term Woads was created for the film because the producers felt the term Picts didn't sound right. The word comes from the blue plant that the Picts may have used to paint themselves prior to battle.
Most of the major battle scenes were filmed using 18 cameras simultaneously. Apart from the mounted cameras, camera operators also dressed as extras and shot from within the action. Cameras were also mounted on shields, swords and horses.
Costume designer Penny Rose prepared for the film by studying the famous book "The Bog People: Iron Age Man Preserved" by P.V. Glob. Glob discovered both Tollund Man and Grauballe Man in Denmark, both dating from roughly 400 A.D., and both with almost perfectly preserved clothing.
According to Ioan Gruffudd (Lancelot), it took him months to grow the "scraggly" beard his character sports during the film. In addition, due to his Celtic heritage (Gruffudd is Welsh), the beard kept growing in red and had to be "painted" each day before filming, to match his brown hair.
When Antoine Fuqua took over the project, he wanted Daniel Craig to play Arthur but was overruled by producer Jerry Bruckheimer, who believed that Clive Owen was going to be cast as James Bond, which would greatly increase the film's commercial shelf-life on DVD.
The X and P seen on soldier's shields are not the Roman letters X and P but the Greek letters Chi and Rho, the first letters of the word Christos. This was the sign that the Roman Emperor Constantine had placed on his soldiers shield, and identifies the soldiers as Christians.
The plot to this movie wherein a battle-weary, elite team must go behind enemy lines to rescue someone of importance as their final mission, is nearly identical to the plot of director Fuqua's previous movie, "Tears of the Sun".
The replica of Hadrian's Wall built for the film was a kilometer long, nearly 40 foot high, with a ten foot wide walkway on top and took a total of 300 crew over four months to construct. Director Antoine Fuqua was determined not to use CG to create the wall as he wanted the actors to be able to see it and stand on it.
The trivia item below may give away important plot points.
Originally, there was no wedding scene at the end of the film; the scene on the battlefield with Lancelot's (Ioan Gruffudd) body is longer and involves a short monologue from Merlin (Stephen Dillane), where he tells Arthur (Clive Owen) he hasn't failed his knights despite the death of Lancelot and Tristan (Mads Mikkelsen). This scene is then followed by the funeral scene, which is also longer, with Bors (Ray Winstone) giving a short monologue. This is then followed by a scene of Lucan (John G. Brennan) trying to remove Excalibur from a stone. He fails, but Arthur tells him that one day he'll be strong enough to do it. Black smoke then rises from Lancelot's pyre and there is a fade to the slow motion shots of the horses riding. However, after several poor test screenings, the audience's biggest complaint was that the ending was too melancholy and needed a scene to finalize the romance aspect of the story. As such, the wedding scene between Arthur and Guinevere (Keira Knightley) was added. Director Antoine Fuqua dislikes the new ending, and on his DVD commentary states that he much prefers the original, darker ending.