Backed by the Pentagon: King Mohammed VI of Morocco, where the movie was filmed, is a good friend of Ridley Scott and personally provided the movie with around 1500 military personnel and equipment.
California Doubling: Huesca, Spain stands for France, Seville stands for Jerusalem, and Morocco stands for any exterior shot in the Holy Land.
Casting Gag: At one point, Sibylla describes one of her rings as being from France and says she's never been there. She's played by a French actress.
Cowboy Be Bop At His Computer: An article incorrectly described the film as pandering to Osama bin Laden, and it was later found out that the journalist hadn't even seen the screenplay. After the screenplay was leaked, another article claimed that the film depicted Muslims as stereotypically stupid, backwards-thinking and unable to think in complex forms. These allegations made King Mohammed VI of Morocco worry for Ridley Scott's safety and he provided him with four bodyguards. Ironically when the movie was released, Scott received many letters of thanks from Muslim groups for the even-handed depiction of the religion.
The reason the theatrical cut was so much shorter than the Director's Cut. Fox wanted a Gladiator style action movie with a romance subplot, rather than the political drama Scott and co created. On top of that, they thought audiences wouldn't be able to handle a 3 hour film, disregarding high grossing films like Titanic (1997) and The Lord of the Rings. The theater-released version was panned, yet the Director's Cut was critically acclaimed as one of the best movies of the year.
Ridley Scott wanted the character of Sibylla to become a nun at the end of the film but the studio insisted it end with her and Balian ending up together.
Ridley Scott used the cue "Valhalla/Viking Victory" from The 13th Warrior for this film. Slightly controversial, given the director's turbulent relationship with The 13th Warrior's composer, Jerry Goldsmith when they worked together on Alien & Legend (1985) that saw Scott cutting off a large part of Goldsmith's music on the former and re-using parts of Goldsmith's earlier score from Freud; while simultaneously throwing out Goldsmith's entire score in favor of Tangerine Dream's music for the latter. Bitter and upset by the rejection, Goldsmith never spoke to Scott again as a a result even unto his passing.
Fake Brit: The American Edward Norton gives Baldwin a British accent. The Irish Brendan Gleeson does likewise with Reynald.
Follow the Leader: Was a part of a wave of films inspired by the success of Ridley Scott's prior historical battle epic Gladiator, with this film's marketing getting a lot of mileage out of highlighting the connection. Then again you can trace this trend's lineage back to Braveheart and even further if one wishes to Robin Hood: Prince of Thieves which led to contemporary interest in Medieval adventure/epic films.
Playing Against Type: Eva Green at the time had played mostly Femme Fatale characters in French films - something which she was reportedly not happy about. Thus Defrosting Ice Queen became one of her character types. Likewise, Brendan Gleeson has made a career mostly playing grizzled, no-nonsense, and nonetheless noble law enforcement types. Here, he plays a corrupt, truly monstrous crusader.
At the start of the project, KOH originally began as a Russell Crowe vehicle called Tripoli. Screenwriter William Monahan (The Departed) had a script written, Scott signed on to direct, 20th Century Fox greenlit it, sets and art assets were being made and then things went nowhere. After two tries of getting it off the ground, Monahan began writing Heaven after Tripoli fell apart and Scott always wanted to do a movie about the Crusades.
The film was pretty much hit with Executive Meddling from the start, with the execs being very uncomfortable with the length of the script and the subplot of Eva Green’s Princess Sybilla’s son, who briefly ruled Jerusalem after King Baldwin (Edward Norton) dies. In Scott’s words on the 4 disc DVD set, he mentioned that studio heads said that the plot “went off on a tangent”. The studio demanded Monahan to write two different versions of the script: One with and without the kid. Scott and co. shot the former.
Filming was actually pretty smooth, save for an instance in which Orlando Bloom came down with the flu and suffered some hand injuries.
When filming wrapped up, Fox was bothered by the length of the cut that Scott had presented them (around 186 minutes) and forced him to cut the film down to a measly 145 running time, exercising the plot about Sybilla’s kid, among many other scenes. Their reasoning was that audiences couldn't handle a three hour film, disregarding successful long movies such as the studio’s own Titanic (1997) and The Lord of the Rings. They also mismarketed the film, making it seem more like Gladiatorset in the Crusades, rather than the Drama that was made. This backfired, resulting in poor box office returns and mediocre reviews (though it did fare better in international markets).
Luckily, the film found new life on video in the form of the Director's Cut, which restored the original running time and as a result, received much better reviews than its theatrical version.
Uncredited Role: Edward Norton asked not to be credited as King Baldwin, as he spent his screentime behind a mask. However, his name was put back in the video releases of the film.
Russell Crowe was supposed to cameo as Richard I but couldn't make it due to a scheduling conflict. Iain Glen plays him instead.
Edward Norton was actually the first choice for Guy. Upon reading the script, he asked to play King Baldwin instead.
The first draft of the script opened directly after the shipwreck. The screenwriter William Monahan had wanted to open with the death of Balian's wife, but feared it would make the movie too long. When Ridley Scott came on board, he told Monahan not to worry about length and thus the film opens with the death.
Many ideas in the finished film were incorporated from another project Ridley Scott had first put into pre-production called 'Tripoli'. The project was falling apart around the time the Kingdom of Heaven script came along, so Scott opted to work on the latter instead.
Alternate endings were filmed, two of which featured Balian arriving back in France alone. As noted above, Sibylla's planned fate was to become a nun to atone for her sins of adultery and murder. But the studio insisted she end up with Balian.
Hans Zimmer was originally attached as the film's composer, but was replaced by Harry Gregson-Williams.