Factual error: The crescent as emblem on Saracen pennants is anachronistic as it appeared on Islamic military flags no sooner than the 15th century A.D.
Factual error: The Patriarch of Jerusalem was (and is) not addressed as 'Your Eminence', which is reserved for Cardinals, but as 'Your Beatitude'.
Factual error: The title (as opposed to the name) is spelt 'Marshal', not 'Marshall' as it appears in the caption when Balian first meets Tiberius.
Factual error: Jerusalem isn't situated in a dry barren desert as it is in the movie. The view East from the walls of Jerusalem is toward the Garden of Gethsemane and the Mount of Olives (from where Saladin attacked on 20 September 1187).
Factual error: It is mentioned that Saladin has crossed the Jordan River and is on his way to Jerusalem. Balian then rides to Kerak to defend the city. But Kerak is situated East of the Jordan River and South of where it runs into the Dead Sea, so Saladin would reach Kerak long before he crossed the Jordan River.
Factual error: The warrior-monks of the Hospitaler and Templar orders were not priests, although they did have attached chaplains. The Hospitaler should therefore not have been able to give Godfrey the Last Rites.
Factual error: In 1184 Golgotha wasn't a barren hill outside the city walls (where Balian goes to reflect in solitude). It was in the middle of the city and there was (and still is) a church on the site.
Factual error: Before the battle of Kerak we see the city with snow capped mountains in the background. There are no mountains that high visible from Kerak.
Factual error: Prior to the battle with Saladin, there is a shot of the crescent moon. A star is shown inside the disk of the moon, but it should have been blocked out by the moon's presence.
Factual error: When Balian arrives in Ibelin, on the wall inside the manor house, he's watching the painting depicting the Dance of Death, with the writing 'quod sumus hoc eritis'. However, the earliest known Dance of Death (Danse Macabre) paintings are from the first half of the 15th century. This motif developed during the late medieval period, inspired by the memory of the Black Death.
Factual error: Balian is depicted in the start of the film to be from France. He was actually a Poulain, a Frank having been born in Outremer.
Factual error: In the beginning of the movie during the burial scene, it looks like a modern community in the background.
Suggested correction: You don't see a "modern" community in the background. You see a few houses, but nothing to indicate anything that it's not part of that time period.