Revealing mistake: When Lucilla takes her hand and closes Maximus's eyes after he dies you can clearly see him blink. (02:19:55)
Revealing mistake: After the final fight scene, where Maximus is dead and on his back in the sand, his armour would have made his head droop horribly backwards. To avoid that, the filming crew put a pillow of sand under his head to raise it about three inches. (02:20:10)
Continuity mistake: At the end of the movie when Maximus is lying dead, and Lucilla asks who will help carry his body. Her bracelet on her arm is positioned differently than right before she asks the question when she is looking around at the crowd. (02:20:10)
Continuity mistake: During the final scenes, when Maximus had died and his body is lying on the sand, we can see both the slaves and the Praetorians forming a semicircle around Maximus. When Quintus asks for help to carry Maximus body, during the second it takes long to raise it up (shot change), the slaves have moved and the Praetorians are forming a perfect honor corridor through which Maximus's body is about to go by. (02:20:55)
Continuity mistake: During Maximus's death scene at the end you can clearly see the entrance that Commodus and Maximus entered the arena through in the floor of the arena. After Juba is done burying the figures of Maximus's dead son and wife, you can not see the entrance anymore when he is walking away. (02:21:00 - 02:22:55)
Revealing mistake: When Proximo is killed by the troops, right after he pronounced his motto "Shadows and Dust", he's replaced by a dummy when they're about to stab him, as revealed by his different hairstyle and thinner build. (02:27:41)
Factual error: At several points in the movie you will see speeches to a large crowd. These take place at the Piazza San Pietro. This square however is late Renaissance. Connected with this is the columns you see in these scenes. They were designed by the Italian artist Bernini, and the film crew didn't even remove the statues of all the popes.
Deliberate mistake: The historically inaccurate portrayal of stirrups in the film was actually due to the stuntmen enacting the cavalry charge in the initial battle scene. Apparently the stuntmen refused to ride the horses over the forest terrain at full gallop without stirrups because it was far too dangerous for both horse and rider. (Galloping a horse through forest or any uneven terrain is incredibly dangerous.) Stirrups were granted as a concession to the stuntmen on the grounds of saftey. Since they were included in this scene, the film makers decided to allow them in all other scenes where necessary. (Only seven stuntmen were used in the filming of these scenes - all the other riders are just CGI copies.)
Factual error: Women were not allowed to be mixed with men. Only Vestales could stay where men were. Women could see the games just from the last ring-level of the Colosseum.
Factual error: Several men, most notably Marcus Aurelius, are long-haired (for male standards) in the movie. In Roman fashion, men were expected to use their hair short. Male long hair was seen in a very bad light, especially for an emperor.
Factual error: There are several points in the film that show horses with saddles and stirrups. Pretty odd as the stirrup didn't arrive in Europe from China until the 3rd or 4th Century at the earliest.
Factual error: Early in the film Maximus walks through a cereal crop trailing his hands against the heads of grain. Except that dwarf varieties of cereal were only bred in the 20th century. Before this a crop would have been up to a man's shoulders.
Suggested correction: No doubt the scene was shot with a modern variety, but it turns out that it is a good approximation of the wheat grown at the time of the story. Two varieties of wheat grown in ancient Rome, the Emmer and Eikorn varieties, reach only 2-3 feet at maturity. These were originally wild wheats that had been cultivated for 8-10 thousand years BCE.
Factual error: As the Gladiators are being led into the Colosseum for the first time, an elephant is led across the background. Although the Romans used elephants in the arena, they used African elephants, and the one we see is an Asian elephant.
Continuity mistake: At the beginning of the film, when the Romans are about to fight the Germanians, a shot of some soldiers standing beside a war machine is shown. In the background, you can see that the fires for the archers are already lit. The next shot then show the same fires being lit and you can tell they are in the same place as the ones previously shown.
Revealing mistake: In the Moroccan prison the iron bars are electric arc welded. As a blacksmith, I can easily spot the visual differences between electric arc welding (a modern technique) and pierced bar joinery such as the Romans would have used.
Revealing mistake: During the first battle the Romans had with the Germans, they show a scene in slow motion with very emotive music that shows the massacre in the forest. Look closely at all the Romans and you will see one fall to the ground, then, as if it was a rewind, come back up again - and then fall again.
Revealing mistake: In the shot of the discussion (literally) over the dead body of Marcus Aurelius (horizontal in the foreground), the "corpse" is still breathing. His belly is rising slowly up and down.
Continuity mistake: After Maximus's family is killed and he is being taken away, he has flashbacks, but one of the images is of him being chained up against the wall, right before his final battle with Commodus - a scene which hasn't even occurred yet.
Continuity mistake: When Proximo gives Maximus his armor the horses have wings. After that they do not.
Continuity mistake: When Maximus stabs Commodus in the neck, in one shot we see his whole neck, and there's no knife in it.
Suggested correction: This movie is not based upon facts. Many element were fictionalized. This is just example of fictionalized things.