The battle of Castlegard never took place. But the crew of the movie visited various European castles from around that period (the late 1300s) to make the castles and towns look as realistic as possible
A group of medieval re-enactors were used for soldiers in battle sequences.
The film was originally set to open in April 2003, but due to poor test screenings Sherry Lansing the head of Paramount Pictures at the time ordered that the film be re edited in the process losing a crucial subplot that is touched on in the final version involving David Thewlis' character and also Jerry Goldsmith's score was replaced because he was not able to return to the scoring stage due to health reasons.
Frank Cappello wrote an uncredited draft of the script and his name appeared on a few of the original teaser posters and trailers along side credited writers George Nolfi and Jeff Maguire.
Twice in the movie (first when Lady Claire is reunited with the French knights, and later in the final battle), a French knight's shield has the Québec flag painted on it. These scenes where shot in Québec, along with every 14th century France scenes.
The film was originally slated to be released in the fall of 2002, however the studio was not happy with the Richard Donner's cut of the film, which included a Prologue explaining the disappearance of the Billy Connolly character in the film and contained Jerry Goldsmith's original score for the film. Donner was then forced to re-cut the film by Paramount and asked Goldsmith to edit down his score to the re-cut version of the film, which also prompted another release date by the studio to March of 2003. Paramount and particularly studio head Sherry Lansing, was again unhappy with Donner's second cut of the film that he had delivered which completely had eliminated the Billy Connelly prologue, which was essential to the both the Michael Crichton novel and the film's back-story, which was originally scored by Goldsmith as a cue called "The Dig" and the musical recording slate number of 1M1. Donner was forced to re-cut the film once more and the film was again delayed to unspecified date and again Goldsmith was asked to return to the project. At this point, Goldsmith's health was deteriorating due to cancer and had recently begin to score Looney Tunes: Back in Action (2003) for his friend Joe Dante, a project which required the assistance of composer John Debney for additional music and would also be his last score as he would pass away on July 28, 2004. Donner really wanted Goldsmith to stay on, but could not for those reasons and liked the score that he had written for the first cut of the film. Paramount then hired composer Brian Tyler, who had written the music for the film, The Hunted, which was released that March in place of Timeline. Tyler would score almost all the identical scenes in which Goldsmith originally scored and each score recorded by both Goldsmith and Tyler are the same length at 74 minutes. The final cut of the film would be 116 minutes from it's original 136 min cut, mainly the Billy Connelly prologue clearly absent from re-cut version and the final cut, which proves that the film was clearly interfered with by the studio. Goldsmith's and Tyler's music would be released respectively by Varese Sarabande records later on.