Goofs

After the first part of the Saxon army is destroyed, the second part enters the battlefield. But somehow all the dead bodies are gone.

At one point, when Arthur is talking to Tristan, his hair changes from being in front of his face to brushed to the side and then back to in front of his face again between shots.

At one point, Guinevere is wearing a dress that has one shoulder bare, but in the next scene, the same dress has the opposite shoulder bare.

In the final battle, a single Saxon survivor from the group sent inside Hadrian's wall partially opens the gate. The shot changes to inside the wall and the gate is fully open. A following shot has the Saxon army moving forward toward the wall and the gate is now closed.

During Arthur and Lancelot's discussion before they leave on their mission, the lighting falls on the left side of Arthur's face in close up, and the left side of Lancelot's, despite the fact they are facing each other. In the wider shot moments later, the right side of Arthur's face is illuminated (as it should have been all along).

Pelagius did not advance a theory of political freedom, but resisted the doctrine of original sin, arguing that one was able to perform good works and achieve salvation by sinlessness alone without requiring spiritual Grace. It was declared a heresy of the Roman Church in 418 A.D.

When Arthur first meets Cerdic he is on his horse standing atop a hill holding the Legion Eagle standard. He plants the standard in the ground and leaves it on the hill unattended and goes down to meet and talk with Cerdic. No Roman commander would ever leave the Legion eagle unattended as losing the Eagle was considered the ultimate loss and disrespect to the legion. In fact, the legion Eagle had a dedicated bearer and this was entrusted to a very senior and well respected legionary.

During the final battle, these is no one to open the gate in Hadrian's Wall, it just seems to open and close on its own. However, the extended edition shows that at least Jols and Ganis stayed behind, possibly to work the gate mechanism.

As the knights prepare to head north to rescue the Romans from the estate north of the wall, there are several shots of the gate north being opened. The scene makes it clear that the gate is almost never opened or hasn't been opened in a long time. The bar has to be hammered free and is covered in dust, the hinges are rusted, draft horses are needed to open them, etc.

If there are villas north of the wall (there weren't), the gate is so seldom used.

The winter scenes were clearly filmed in summer; there are leaves on the trees, nobody has visible frosty breath, and the snow is clearly fake.

During the final fight, there is blood on Tristan's clothes, but in the next scene it is gone.

In the final battle, the Woads are shown using trebuchets. Catapults would have existed in Europe at this time, but not trebuchets. The traction trebuchet did not reach Byzantium from China until sometime in the late 6th century, over 100 years after the time of the film, and the counterweight trebuchet (the one used in the film) did not reach Europe until the 12th century (over 700 years after the time of the film).

Arthur and his knights ride horses using stirrups. Stirrups were invented in China around the 4th century and were not seen in western Europe before the 8th century, two or three hundred years after the events depicted in the film.

The Pope did not have the power to give land to a people in the fifth century. This was not possible until nearly 400 years later.

When warning Bishop Germanius before going on the final mission, Arthur makes reference to "papal armies". Papal armies did not come into existence until many hundreds of years later in the late middle ages.

Throughout the movie, the politics of Rome are portrayed as if the Pope ruled the empire: A bishop, rather than a military officer, is sent to deliver the knights' discharges, and the decision to send them on one last mission is made by the Pope alone. In reality, both the Western and Eastern Empires were ruled by Emperors. The Pope, on the other hand, was not even the head of the entire church (let alone an empire) at this time - he was still just the Bishop of Rome. While he was highly regarded by the rest of the bishops in Christendom, it would be another 600 years before the Pope was recognized as the head of the entire church.

After they rescue Guinevere and Lucan, Lancelot approaches Arthur and says "If the Saxons find us we will have to fight." His lips don't move along with the words.

When the Woads trap Arthur and his men with barbed-wire-type enclosures, Bors can be seen yelling, however, there is no sound.

Just after the end of the first battle with the Woads, Bors draws back the curtain of the carriage to look in on the Bishop. As he does so, the leg and boot of a crewmember is visible inside the carriage.

During the final battle, the camera pans all around the inside of the wall. As the camera pans the very top of the wall, where the stones are staggered, another camera is moving on a sort of zip line as the battle rages on.

Cerdic invades from the North in the film, but in historical fact, he invaded from the South, as he would later found the kingdom of Wessex. Also, the first Anglo-Saxons did not initially invade; they were invited to Britain to help defend the Britons against raiders from the Irish sea, the Scots, Gaels and Picts. The Battle of Badon hill took place approximately 80 years after the Roman withdraw from Britain in 496 A.D and Baden Hill itself is nowhere near Hadrian's wall, it is much farther South, most likely on the hills surrounding Bath.

One of the knights flies a hawk in several scenes. The hawk is a Harris' Hawk from the Americas, which had no commerce with Britain until nearly 1000 years later.

Along with it being factually inaccurate, it makes no sense to send a member of the Roman aristocracy and all of his family to live in a land unclaimed, unoccupied and undefended by the Roman army.