Revealing mistake: At the end, when Maximus had gone to afterlife world of Elysium and was meeting his wife and son, both the wife and the son put their hands up as to shield the sun from their eyes. You can clearly see that their hands are not blocking out the sun, because the shadows are not over the eyes. (02:19:45)
Continuity mistake: In one scene, where you see a view of the Colosseum and its flags, all the flags are pointing towards the middle and that's strange keeping in mind the wind comes from one direction. (01:11:45)
Revealing mistake: When Proximo is having his speech for the slaves as he says "And as your mothers were there at your beginning" there is a shot of a man throwing a spear at another man. Look at the spear as it flies through the air. It wiggles as if it is attached to a wire. (00:48:40)
Continuity mistake: When Commodus and Lucilla are talking while Commodus sits on his throne, the shots change from in front of Lucilla and behind her. When it's behind her it is the wind is blowing through her shawl. When it's in front of her it's not blowing. (01:00:50)
Revealing mistake: When the Roman soldiers throws bowls of oil on the servants and set them on fire, the protective mask on the burning servant standing up is visible. (Extended version only). (02:19:00)
Continuity mistake: When Commodus arrives and asks Aurelius if he has missed the fight, Aurelius' hair is blowing in the wind. When it cuts from behind Aurelius his hair is not moving. (00:15:50)
Continuity mistake: During the first gladiator battle Maximus grabs another gladiator's sword by the blade. Two shots later he is holding the sword by its handle with no time to change grip. (00:54:20)
Continuity mistake: When Maximus comes back to his tent after seeing Aurelius dead he tells Cicero to wake Gaius and Falco. Then he says "Sword" and Cicero gives Maximus something and walks away as Maximus turns around. When it cuts Maximus turns around again. (00:37:05)
Continuity mistake: During the battle of Carthage, Hagen stands alone with an arrow in his shield, couple of scenes on, no arrow, couple of scenes on again, an arrow hits his shield. (01:21:20)
Revealing mistake: When Maximus is being taken to be executed he escapes - when he whacks the last man round the face look closely and you see he slashes about a foot away from the soldier's face. (00:38:45)
Audio problem: When Commodus is talking with Lucilla before the Battle of Carthage as he is saying "I could announce the dissolution of the senate...". It cuts from behind him and he says "...are the people ready?", however his lips don't synch up with what he says. (01:32:25)
Revealing mistake: When Hagen pretends to choke on the beans, just after he finishes laughing, there is a shot of him sitting between Maximus and Juba. You can see his non-Roman underpants. (01:36:35)
Revealing mistake: When Maximus is riding against the Germanians, as he meets the first Germanian, he hits the Germanian's spear and hits him with his sword. However, the hit isn't even close, but about 30 centimeters from the Germanian. This is even seen without slow motion. (00:09:30)
Continuity mistake: At the slave market when Proximo is checking Juba, he grabs Juba on his wrist above the lock. When it cuts he has grabbed him below the lock. (00:47:20)
Continuity mistake: After Juba has thrown the sword to Maximus, Maximus tries to gather the gladiators by shouting "Single column, single column," then it cuts to him charging on his horse while holding his sword arm out. When it cuts from behind him he is holding his sword arm in front of him instead. (01:24:10)
Continuity mistake: When Hagen is shot in his leg with an arrow he is holding the arrow in his leg. Maximus notices the chariot charging for Hagen and he shouts "Hagen". It cuts to Maximus running against Hagen, but now we can see that there is no arrow in Hagen's foot. When it cuts to Maximus reaching Hagen and pushing him away from the chariot the arrow is back in his leg. (01:22:45)
Factual error: In the scene where Maximus is finding his wife and son's bodies there are two chickens to his left. One of these is definitely a Rhode Island Red hen. This breed of chicken was developed upwards of 1,700 years after Roman times in the US state of Rhode Island. (00:44:10)
Factual error: There's a blackboard in one of the scenes when there's about to be a gladiatorial contest. The Romans may have had blackboards then, but the writing on it is wrong. The sort shown takes time to chip into stone used on statues, etc, and I suppose it would take quite a long time just to write things on a blackboard. The Romans had different writing for things like that, as shown in the graffiti in Pompeii. It's more flowing, and I expect it's quicker to produce. (01:15:00)
Factual error: The last gladiator to be killed when Maximus is chained to Juba holds a trident. This kind of gladiator is called a "retiarius." They're also the ones who fight using nets. The shoulder armour was always worn on the left shoulder, not the right, because left-handedness was frowned upon in Ancient Rome. Also "retiarius" never wore face masks for helmets as it would give them too much of an advantage. Every Gladiator was given equal advantage depending on their specialty. (00:55:25)
Continuity mistake: When the Roman soldier shoots the signal arrow before the attack against the Germanians, you can see his bow twist at least 45 degrees between the shots. (00:07:25)
Chosen answer: No, they are full brother and sister. They both had the same mother and father. Incest was not exactly normal at that time, but it stretches back within the imperial families as far as Caligula and possibly earlier. There is no evidence to suggest that the real Commodus was attracted to his sister, it was probably just included in the film in order to make the character seem more disturbed, and also as another reason why he would be Maximus' enemy (Maximus and Lucilla were, after all, once lovers).
The Doctor