At the beginning of the film, when the party is ambushed, a rider charges towards Godfrey. He is wearing a conical helmet, but in the next shot, after Godfrey has dispatched him, his helmet is flat.
Balian's arm was slashed by a sword perpendicular to his arm, however, the injury shown later has the gash going length-wise down his wrist.
When the priest's assistants are burying Balian's wife, the priest instructs them to behead the corpse. One of them picks up the axe but in the close-up of the corpse's face, the axe is still lying on the ground next to her.
The size of the hole made by the sword in the sand when Imad falls after the fight for the horse changes; from large and uneven to even
During the battle for Jerusalem, the crescent moon and the star in the banner change positions during a short period of time. First, the crescent is horizontal, with the star a short distance above it. In the next scene, the crescent is on an angle, and the star is where the unlit part of the moon would obscure it.
Contrary to what is shown, the casualties among the defenders in Jerusalem were actually only a few each day until the final fight. This was typical for close fought city or castle defenses, and reflected the extreme advantage of fighting from thick high walls with well placed towers.
Trebuchets throw their projectiles in a notably high arc, not the low direct path shown.
Patriarch Eraclius is depicted as a coward who advocated abandoning Jerusalem and its inhabitants in order to save his and Balian's lives. In actuality, Balian wanted to leave the city, as he had come only to evacuate his wife and children and had sworn an oath to never take up arms against Saladin in order to cross the siege lines. Eraclius absolved him of his oath and encouraged him to fight Saladin long enough to negotiate a truce for the lives and freedom of Jerusalem's citizens. He then had all the churches' silver stripped down and melted into coins to pay the defenders. After the siege, Eraclius and Balian collected money from the city's wealthy to pay ransom for 18,000 inhabitants, and offered themselves (in vain) as hostages for the remaining 15,000 who couldn't pay.
In the movie we see Mullah (Khaled Nabawy) wearing clothes with inscriptions of the Quran on the arms. In Islam, it's completely forbidden to write any of the names of Allah, or any verses from the Quran on clothes. Although it is allowed to write "Allah is the great" or "there is no God except Allah and Muhammad is his messenger" on flags.
In the film, King Baldwin IV (Edward Norton) wears an iron mask to hide the horrific signs of his leprosy, but the real Baldwin IV "refused to hide himself as king even as the disease consumed him".
In the directors cut version, Balian is in Jerusalem, praying where Christ was crucified - you see him burying his dead wife's silver necklace (cross). Later in the movie, you see him pulling out the ring that Sibylla gave him and kissing it - not the cross of his late wife.
In the beginning of the film the blacksmith is hammering a hot piece of iron which he puts in water and immediately starts to hammer again. The iron is red hot even after being dropped in water.
King Baldwin IV speaks surprisingly fluidly considering, when Sibylla removes his mask after death, he's shown to have a large part of his upper lip missing.
Throughout the siege of Jerusalem, when the defenders use projectile weapons such as bows, trebuchets, crossbows, etc., the command given to release the projectile is "Fire!". This command did not come into use until the advent of matchlock firearms in the mid-15th century. The correct command would have been "Loose!".
During the 12th century, the Knights Templar wore the Maltese cross on their habits. It wasn't until a century or so later that they were ordered to change to the Roman cross. For reasons unknown, this is an error that Hollywood has always made.
The so-called 'Templar' who attacks Balian before the battle of Hattin (in 1187) wears a white surcoat bearing a black cross: the arms of the Order of St Mary of the Germans (aka the Teutonic Knights). This order was not founded until 1190 at the very earliest.
In the Director's Cut, Sibylla tells her son, soon to be Baldwin V, in his geography lesson, that the King of England is Richard, the son of King Henry. Richard I did not succeed his father until 1189, three years after the death of Baldwin V.
The trebuchets are shown with metal axles for the throwing arm (this is most visible as the camera moves past a trebuchet before Balian's knighting speech in Jerusalem). The technology of the time did not permit the creation of such large pieces of metal. Throughout medieval times a trebuchet axle would have been made from a thick timber.
When the vultures are feeding following the Battle of Hattin, the species shown is the Griffon Vulture, but the audio is of Sandhill Cranes.
In some scenes involving horses, modern orange cones can be seen on the ground directing the riders on the path past the camera to follow. This has been corrected for the Director's Cut DVD.
In front of Reynald's castle, when Saladin's army comes, a yellow plastic pole that marks a stopping point for the foot soldiers is clearly visible. (This has been corrected for the Director's Cut DVD.)
A camera can be seen briefly to the right during the fight Balian is ambushed by the three knights sent to kill him.
When the Muslims are praying near Jerusalem they are praying towards the setting sun, west, not towards Mecca which is to the south southeast.
In the movie Jerusalem is shown to be in a flat, sandy desert. Jerusalem is actually set on top of a mountain (Mount Zion) with massive valleys filled with trees, and other greenery surrounding the city walls.
The castle of Raynald of Chatillon, called simply "Karak" in the movie and known as "Crac des Moabites" at the time, is shown on a modest rise above a plain. It actually sits atop a ridge surrounded by fairly steep valleys.
When Balian is building the timber water channel he places the lower level duct on top of the higher one. This should be the opposite way round as in its current state any water running down would run under the lower duct and consequently be lost.
Saladin's recitation of Al-Fatiha (the first chapter of the Holy Quran) is not complete. After the surrender of Jerusalem, we see Saladin reciting the Sora, but he does not finish before he starts another one.