Continuity mistake: After Lucius quotes Virgil, he kills a man who collapses on a chair. When he lies dead, there's a leg or armrest on the floor parallel to his body. A shot later, it's perpendicular.
Continuity mistake: When Lucius steps in the water to see his wife's corpse, his hairstyle around the forehead changes between shots before he is splashed by water.
Continuity mistake: During the riots night in Rome, Macrinus and Caracalla talk to Geta, his monkey on his shoulder. The position of the monkey is inconsistent in every single shot.
Factual error: Caracalla and Geta in this movie are decadent mad kings, but that's a portrayal that has no foundation in history - here they look more like their successor Eliogabalus. Caracalla in particular, who was the elder brother, wasn't an effeminate sybarite plagued with syphilis; on the contrary, even by his detractors, he was mostly remembered for being, or at least acting, very soldier-like; "Caracalla" was his nickname, after a military mantle.
Factual error: Much like its predecessor, this movie sorta speedruns through emperors; Geta and Caracalla here are shown as both ruling Rome as "twin emperors" in 200 AD, and die within a couple of days of each other, betrayed by Macrinus, who dies the same day. None of that is anywhere close to how things happened, to the point that discussing dates is sorta pointless; nothing resembles history if not in the loosest sense. Macrinus in this movie is never even formally proclaimed emperor, as opposed to him ruling for at least a full year.
Factual error: The movie begins in 200 AD, and the victorious general Acacius celebrates triumph and reports to the twin emperors that he conquered Numidia in their name. This may be less of an accomplishment than it appears when you consider that Numidia had already been a Roman province for centuries.
Other mistake: Macrinus and one of his high-ranking friends are discussing Lucilla's son, who disappeared when Commodus died. The guy says that Lucius disappeared when he was "about 12," but in the original Gladiator, he was barely about to turn 8. They also say these events happened 16 years prior, but, again according to the movie lore (without even looking at history), he died in 180 AD, and this movie is set in 200 AD.
Continuity mistake: When Macrinus is poisoning Caracalla's mind, telling him about supposed plans of his brother to use him as a scapegoat, Caracalla shouts, "That's a LIE, he's... he always LIES." The cup suddenly switched hands.
