Continuity mistake: When Balian is talking with Tiberius after denying the King's proposal, watch Balian's clothing. His chain mail is visible on both sides of his shoulders in one shot; we cut to Tiberius for one line (I believe it was, "Jerusalem has no need for a perfect knight") and when we cut back to Balian, his cloak is now covering the chain mail completely.
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.
Add timeJacob La Cour
Other mistake: When Balian talks to God on the hill where Jesus died, after he says his line, the next shot is him sitting down overlooking the empty valley below. A white light travels from right to left going 45-50 mph. Nothing back then could go that fast, and even if anything could, a torch is yellow and red, and even if it could be white, no rider can ride that fast with a white-light torch and keep it from going out - leaving us to assume it's a car.