Doing It for the Art: Mel Gibson chose to bankroll the film with his own money, shooting it entirely in Aramaic and Latin, and originally didn't even want to include subtitles. It's easy to forget, in light of the film's huge box office, that this was actually a huge financial gamble.
Dyeing for Your Art: Jim Caviezel had to go through extensive hair and make-up (at times, full-body) and would also suffer as much as Jesus himself: He had to carry a heavy cross, injuring his shoulders (and once his head, as Caviezel tumbled and the thing fell along), got headaches from the thorny crown, had to stay with only a loincloth in a cold environment for the crucifixion, was struck by lightning (twice), and during the flagellation, the guy playing the guard accidentally whipped Caviezel's back at least once (ironically providing reference to the make-up crew, which had to match the injury...). Thus sometimes the expression of anguish is totally real.
Fake Nationality: James Caviezel (Jesus Christ) is American, Maia Morgenstern (Mary) is Romanian, Hristo Shopov (Pontius Pilate) is Bulgarian, Monica Belluci (Mary Magdalene), Claudia Gerini (Claudia Procles), Luca Lionello (Judas Iscariot), Luca De Dominicis (Herod Antipas), Mattia Sbragia (High Priest Caiaphas), Rosalinda Celentano (Satan), Toni Bertorelli (Priest Annas ben Seth), Sergio Ribini (Dismas, the repentant criminal), and Francesco Cabras (Gesmas, the unrepentant criminal) are all Italian.
During the carrying-his-cross scene in The Passion of the Christ, Jim Caviezel dislocated his shoulder when he collapsed and the cross fell on him. He insisted that the take be kept in the final film, so that the pain Jesus was supposed to be experiencing would seem more real. (Caviezel also noted how half the blood dripping from his mouth in that take is Kensington Gore and the other half is his own)
During the flogging scene, Caveziel was wearing a protective guard on his back while being whipped, but on the last blow the guard slipped and he was whipped for real.
To prevent injury the cross was on pads of sorts to lessen the impact as it was dropped to the ground. While recording it actually showed the cross bouncing a couple of inches off the ground. It was left in because of its simple effect.
The original plan was to have no subtitles during the whole film. Remember, the entire film is in Aramaic and Latin. This idea was scrapped because test audiences insisted that at least the important lines should be understandable rather than guess-work from the character interactions.