Corrected entry: The Saxons are seen invading to the north of Hadrian's' wall. In reality, they invaded to the south of it, and that is the reason why they managed to take control of Southern England.
Corrected entry: Arthur and his men are charged with passing Hadrian's wall and taking the Roman family to safety; yet at that time in history there is no way a Roman family would be in Scotland; they certainly wouldn't have had a castle (no matter how small) and a peasant settlement. Missionaries or not, the Scots would have driven them out.
Corrected entry: Fifth century Saxons never had crossbows, they weren't introduced anywhere in Europe until they came from Asia around the 11th/12th centuries.
Corrected entry: In the final battle the defenders use the trebuchets left behind by the retreating Roman army. But trebuchets require a lot of technical experience to use effectively. With the depart of the Roman empire these 'high-tech' weapons had become useless.
Corrected entry: A very common mistake in movies playing in historical times is domestic animals - horses in particular - shown in the film are not coherent with archaeological findings; most often, they are way too big. While few Roman horses of the time the movie is supposed to take place reached a size of 1.6m, most horses of the native tribes were much smaller (about 1.3m) and would nowadays be considered as ponies. The horses shown in this and other similar movies are typical modern sport horses.
Corrected entry: The Battle of Badon Hill must have occurred near a hill, as the name says, and not in front of Adrianus's Wall where there is no hill anywhere, as we can see in the final battle of the movie.
Corrected entry: The Saxons are seen coming with a large fleet to Britannia. This is not true because the Saxons came ship by ship to Britannia, and not with a large fleet.
Corrected entry: The weather in the film is portrayed as wintry throughout with snow, ice and blizzards. Yet the tree climbed by the English spy (shortly before he's shot out of it by one of Arthur's Knights) is an oak tree in full leaf that looks like it was filmed in mid-summer. Similarly at one point there is snow falling, yet with a background shot of blue sky.
Corrected entry: Did it escape anyone else how the doors in Hadrian's Wall changed their ease of use? Early in the movie, we're shown the doors opening, and they're made out to be these great, ponderous things that take a long time to open. First the soldiers have to take a heavy mallet to prize free the huge wooden bar holding them shut, remove the bar, and then two huge Clydesdale horses are required to slowly pull them open and then the doors slowly open. And yet in the final battle against the Saxons, Arthur is somehow managing to open and close these doors pretty quickly, and several times in a row, no less. Not to mention how he (or someone else on the good guys' side) now seems to have the ability to remotely operate these doors, making them close behind the Saxons after they enter.
Corrected entry: Jols, the Sarmatians' quartermaster, seems to appear from nowhere and disappear again several times.
Corrected entry: When the knights leave on their quest to save the Roman family, they leave alone; then, at the estate, the Bishop's assistant suddenly appears, with no explanation as to how he got there.