Revealing mistake: When Mr Witt rides out of the Zulu camp in a 2 horse cart at the beginning of the movie, just before it exits, you can see it's a stunt double at the reins.
Factual error: The narrator mentions that the Cheyenne tribe split in half in northern Nebraska. The scenery would suggest otherwise, as there are no mountains that high in Nebraska.
Factual error: In reality, Commodus did not die in the arena - he was strangled in his apartments in 192 A.D. by an athlete who was hired by a group of Senators conspiring against him.
Factual error: At the start of the excommunication scene, the monks are chanting Dies Irae, a thirteenth century Catholic poem, but St. Thomas Becket died in 1170, almost a century before the poem was written.