Michael Crichton, author of the same-titled book off which this movie is based, disliked this movie so much that he refused to licence any more movies based off of his novels. Nobody would gain the movie rights to a Michael Crichton book until Steven Spielberg, long-time friend of Michael Crichton, bought the rights to 'Pirate Latitudes' after Crichton's death.
The battle of Castlegard is not an actual historical event. However, 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
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 2003. Paramount, 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 Connolly prologue, which was essential to the both the Michael Crichton novel and the film's backstory, 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 (2003), 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 its original 136 min cut, mainly the Billy Connolly 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.
Michael Crichton took the unusual step of offering up the film rights for free provided the movie entered into production immediately. Crichton had a back-end deal set up on the basis that his script be used for the film. Ironically, Crichton ended up hating the finished film.
The problem of language is ignored in the film, having a French speaking character. In the novel, however, it is stated that -as in reality- people in 1357 did not speak modern English or French, but Occitane, a language which Marek is fluent in, according to the book. Also, the novel describes some high-tech translator devices the characters put in their ears, which also is absent in the movie.
The film makes many changes regarding Doniger's company and the time traveling device. In the novel, people and objects can be sent to any location and time, unlike the movie that they are "locked" to 1357 Castlegard. Also, Doniger himself is much darker, and actually it is hinted that unwanted or rogue employees can be given "markers", that could send them to places in time for them to die, such as Pompei or the great Kanto earthquake.
The trivia item below may give away important plot points.
The character Andre Marek was stated to be born in 1971. Marek travels back in time to 1357 and lives in that time until he dies in 1382. Since the movie is set in the year it was released, 2003, that makes Marek 57 years old at the time of his death.