In the final scene where the horses are pulling the wagons through the mud the leather traces are connected to the cart by marine type stainless steel quick release shackles and mountaineering type stainless steel screw karabiners.
The Danes use armour and equipment which is (very loosely) based on that used by their Viking ancestors more than a century-and-a-half earlier. In fact, in the 13th century Danish soldiers would have been equipped much like the warriors of any other European country.
The film shows Rochester Castle standing next to a bridge in a totally empty moorland landscape. In fact the castle was (and is) on the edge of the City of Rochester, which was already a thousand years old at the time of the siege, and right next to it is the great 11th-century cathedral of Rochester. On the other side of the bridge was (and is) the town of Strood, plus a number of smaller settlements.
In 1215, Rochester was already a sizable city. When Rochester castle is seen in the film, there is no sign of the dwellings that would have comprised the city, nor of the cathedral, which is a massive building, situated about one hundred yards from the castle. The cathedral was looted by King John's forces, during the siege.
The film's final voice-over narration claims that the rebellion against King John was victorious within a year of John's death in 1216, when the exact opposite is true. Royalists fighting on behalf of John's young son, Henry III, defeated the rebellious barons and their French allies in 1217, and Henry went on to rule England for 56 years. Louis, the French prince the film implies succeeded John as king, never held the English throne.
The film shows forty pigs being herded into the mine under the castle walls, and then burned to make the timber pit-props collapse, bringing down part of the castle. Live pigs are actually rather hard to set fire to. What actually happened is that forty pigs were slaughtered, and their fat was taken into the mine, along with other inflammable material such as straw.
Albany is described a couple of times as a 'wool merchant'. In reality as a Baron he collected money from the land that he owned. No Baron would lower himself to be involved in trade as a merchant, it would have been demeaning to him.
During the historic 1215 siege of Rochester Castle, the Kings forces initially gained access by mining the south east tower in the curtain wall. This method was then repeated on the south east tower of the keep. The film fails to show the Keep is completely surrounded by the curtain wall as well as the first tower's collapse. The castle today still shows evidence of the two collapsed towers, as they were later rebuilt as semi-circular, compared with the original square towers.
The Danes are seen painting their faces blue. This was a Pictish/Scots practice. The blue pigment was extracted from the woad plant (as seen in Braveheart). It was not used outside of what is now the British Isles.
There are numerous errors in the depiction of the Templars. These include: 1) They are shown in armour with surcoats, and armed, whilst travelling on a civilian mission. In reality Templars wore monastic-style robes unless expecting to go into combat, which the Templars were not. 2) The Templars wear surcoats over their armour. Surcoats were not worn by Knights Templar until the 1240s, 30-odd years after the film is set. Before that they wore white monastic style gowns over their armour. 3) Although it is correct that the Templars used a red cross as their emblem, is was a cross patée, which had arms of equal length flaring out at the end. The cross shown here is a Latin cross, with plain arms of which the lowest is longer than the others. 3) Marshal is seeking permission from the Archbishop of Canterbury to leave the Templars. In fact the Templars were not subject to any Church authority except the Pope; Marshal would have sought permission from his own superiors in the Order.
There are a lot of Hungarian stunts in the film, who do shout things in the heat of fights, thankfully the meaning does go with what is happening, and if you don't speak Hungarian you probably don't even notice it, but for Hungarian ears its really funny when you watch it and suddenly someone shouting in your language when you wouldn't expect it.