Goofs

After Lucius bites the monkey, his mouth and chin are covered in blood. It disappears shortly afterward, without any time for washing.

Lucius gets marked by a hot branding iron once he is captured. That mark frequently appears and disappears towards the end of the movie.

When Ravi is healing Lucius after a fight there is no blood in Lucius' face. Ravi asks him to go with him to where they bury rebel gladiators and there a whole side of Lucius' face is covered in blood.

Arishat is shot about the middle of her chest and the arrow is angled up, but when she is floating in the water, the arrow is higher and straight in.

After the conclusion of the battle in Numidia, when soldiers try to arrest Lucius Verus as he emerges from the shallow water beneath the fortress, a cut on his right upper arm bleeds intermittently.

The naval battle is described as "the reenactment of the Battle of Salamis between the Persians and the Trojans." The battle was between the Persians, Sparta, and Athens.

In the beginning of the film, when Lucius is tending to his field in Numidia, pumpkins are growing. At the time, pumpkins grew only in the Americas.

The Praetorian guard and the main legion of the Emperors are clad in purple, and have purple banners. Purple dye was so expensive in Ancient Rome that even Emperor Nero decreed it for his own personal use, and issued death penalty for anyone who dared to wear purple.

Sharks are difficult to transport and keep in captivity, even in modern times. There is no practical way Ancient Romans could have brought sharks into the Colosseum.

The emperor and the crowd raise their thumbs for "live" and lower them for "kill." In reality, the emperor would cover his thumb with his fingers to signify "live." A gladiator could also be spared if the emperor yelled the Latin word for "dismissed" or threw a piece of cloth, indicating mercy. To signal death, the emperor would extend his thumb straight out to the side, symbolizing the sword. Studies of Roman artwork suggest that "thumbs up" was used to affirm the decision to proceed with the kill.

The Roman god of the sea was Neptune, not Poseidon. However, educated Romans spoke and wrote in Greek routinely, and calling gods by their Greek names was a common affectation.

Lucilla and Lucius are called the queen and prince of Rome. The Roman monarchy had been eliminated about 700 years earlier. However, calling Lucilla a "queen" could be a way of criticizing her as a tyrant who wanted to reinstate the monarch. "Prince" meant "principal citizen," i.e. emperor, a title to which Lucius had claim.

Lucius Verus is pitted against a rival fighter standing on top of a rhinoceros, its horns covered in blood. Gladiators only fought men. Bestiarii, who fought animals, were a separate category of combatants. However, it is clear that these emperors do not adhere to the standard rules of gladiator combat.

English sentences are engraved in the walls of the Colosseum and other Roman buildings. It's a convenience for modern audiences, routine in period dramas.

Macrinus tells Viggo to hose Lucius down. There were no water hoses in the time period of the story.

When sparring with Lucius, Viggo is wearing a spiked cestus on each hand and hit Lucius several times, but Lucius doesn't get a scratch on his face or body. The spikes were obviously sharp and made to wound.

After the arena fight with the baboons, Acacius is seen riding a horse in an evening scene with a gibbous moon visible in the sky. The problem is that the Moon is lit from above which would only be the case in the daytime, not after sunset.

On numerous occasions a sword is either picked up from the dirt or swung in the air without making contact, but the sound heard is of a sword being unsheathed when no sheath is present.

Naval battles were only staged in the first year after the Colosseum was built. After the construction of the Hypogeum it was no longer possible to flood the arena.

Trebuchets are used for city defense. The trebuchet was developed in China in the fourth century BCE, but it didn't reach the Middle East until the sixth and seventh century CE. The counterweight-driven trebuchets shown in the film were developed in Europe in the 1100s.

A man sitting a cafe reads a newspaper. Mass-produced paper didn't exist at the time. "Acta Diurna," government announcement bulletins, were carved in metal or stone and posted in public places.

Emperor Caracalla demands that General Acacius conquer Persia. By the time the movie is set, the region was called Parthia.

The Romans emphasize invading Numidia. By the time of Geta and Caracalla's rule, North Africa had been Roman provinces for over 150 years. The real siege of Numidia took place during the Jugurthine War, between 112 BCE and 106 BCE, almost three centuries before the film takes place.

Coming from the port of Ostia, it would not be necessary to cross a river to enter Rome.

The Colosseum appears to be on a hill and towers high above Rome. In fact, it sits on the floor of a low valley between the city's Caelian, Esquiline and Palatine Hills.

When the captured Numidians are taken to be trained near Rome, the landscape is clearly North Africa.