Factual error: The artillery in this movie are counterweight trebuchets, a type powered by a falling weight. The Romans had many spring and torsion powered artillery, such as scorpions, ballistas and catapults, but did not have trebuchets. By the 3rd century BC the Chinese had the "torsion trebuchet", similar to a trebuchet but powered by men hauling on ropes instead of a falling weight; it didn't reach Europe until the late sixth century. The pure counterweight trebuchet as shown in the movie sometime in the fifth century AD probably didn't exist before the late 12th century and the first one in Britain was built in 1216 AD.
Factual error: The Emperor ruled the Roman Empire, not the Pope. Neither he nor one of his bishops would have any authority over Roman provinces or Roman soldiers.
Audio problem: When the Woads are surrounding Arthur and his knights, one of the knight is shouting something, but nothing comes out of his mouth.
Factual error: The scene in which the two armies confront each other on the frozen lake contains several flaws. First, when thick ice is broken with a sharp object like a pickaxe, you merely get a hole through the ice, it will only fragment into large pieces if it is thin. Clearly, this is not the case, as the armies are able to walk on it. Second, ice does not shatter in the way depicted in the film, with cracks travelling outwards a great distance, but just crumbles around the area where force is applied. Third, if cracks did radiate outwards, they would propagate sideways and backwards as well as forwards (like glass does when it is punctured by a small, sharp object), meaning that both armies would end up falling through the ice.
Factual error: Two things are wrong about the trebuchets. While Romans did have siege engines, like the catapult and the ballista, the trenches apparently is a Chinese invention. In any case, it wasn't introduced in Europe until the Middle Ages. Also a trebuchet is a complicated device, much more difficult to operate then it looks. Firing it is easy, but hitting a target certainly isn't. (With modern reconstructions, even when using ballistic calculations, it still takes days of practice to get to a point of some accuracy.) When the Roman army left, the trebuchets were completely useless. In the final battle the Woads nevertheless use them to great effect - impossible.
Factual error: The Romans left England in 410 AD and the Anglo-Saxons didn't arrive in England until the late sixth century. Between these times the Britons were in control of the island. (00:23:55)
Continuity mistake: When the knights & the Bishop are around the round table, the Bishop's assistant is heard saying to Jols (after introducing Bishop Germanius), "A round table? What sort of evil is this?" and he is not on screen. Jols, however, is and he stands as though there is no one talking to him. In the very next shot he is looking at the assistant and speaks to him as though they were talking the whole time. (00:21:50)
Deliberate mistake: From outside, the dungeon where Arthur finds Guinevere has no windows. When the knights force themselves in, it is pitch dark. But in some scenes a window is to be seen in the background, although the jails are one floor down. Even better the cages, in which among others Lucan sits: they are lighted from below. (00:46:20)
Other mistake: The movie starts with scenes from a battle between Romans and Sarmatians. For a few seconds, we see a (very dark) shot of a warrior holding a severed head in his hand. That very same shot is used later in the battle between the Woads and the Sarmatian knights protecting the Bishop. Director's cut only. (00:01:05 - 00:08:30)
Visible crew/equipment: In the scene where king Arthur is on a horse walking across a frozen lake, you can see a huddle of camera equipment in the background. The next shot is from that spot.
Revealing mistake: At the start of the film when the Bishops convoy is ambushed by the Woads Arthur stabs his sword at the ambusher, totally missing but the Woad still falls as if stabbed.
Continuity mistake: When Cerdic is about to kill Arthur on the final battle, look at Cerdic's hair which changes position on his forehead during close-ups.
Continuity mistake: When Cedric holds wounded Tristan to show his triumph to Arthur, the underdog is standing (you see his head at the height of Cedric's), next (when he looks at his falcon) he is kneeling, and when Tristan receives his deathblow, he's standing again. (01:44:35)
Revealing mistake: Despite at least two days of near blizzard conditions there is never more than a few inches of snow on the ground. The amount of snow we see falling should have left well over a foot of snow.
Revealing mistake: Just before the battle of Maldon, the British spy climbs into the big tree and you can see the tree is fake. The spy isn't actually climbing the tree (by grabbing branches), he's using some kind of ladder. (01:36:55)
Continuity mistake: In the shot of Bors (during Venora's singing), Galahad is shown in the back with Gawain being the closest knight to him, a stream directly behind, and a wall far behind. Cut to Lancelot, then to Tristan who is near a wall, then to Galahad with Tristan right behind him and the wall closer.
Audio problem: In the ice battle scene, after the Knights unsuccessfully attempt to make the Saxon army cluster to break the ice, Arthur tells the Knights "It's not going to break". But if you look at Arthur, his lips aren't moving when he says it.
Continuity mistake: When Cerdic calls for the main body of the Saxons to go through the door Cynric is shown drawing his sword, waving it over his head and yelling. In the next shot seconds later his sword is sheathed and he is walking calmly beside his father.
Visible crew/equipment: In the last fight, when the first Saxons enter the door, there is a doorstop visible to keep the door open. (01:47:50)
Answer: Most of them are Friesian or Friesian crosses but but some are Andalusian.