NOTE: This spoiler was sent in by Southern Bellewho calls it a... "Great movie!"
The movie starts with a very brief text of King Arthur's legend; telling us how Arthur and his knights are from a group from the east that was defeated by the Romans. The Romans took pity on the few that were left alive, but in turn, the sons of those left alive would have to serve for Rome for 15 years; it then shows a boy Lancelot riding to meet with the rest of the Romans and the other sons who'd been taken.
Next is 15 years later, we see a caravan carrying a bishop, who has papers that will give Arthur and his knights their freedom, then it shows Arthur, Lancelot, Gawain, Galahad, Bors, Dagonet, and Tristan. The caravan is attacked by Woads. Arthur and co. ride to battle defeating the Woads, who's leader is Merlin (no magic). Arthur and his knights escort the rest of the caravan back to their fortress (not Camelot); there the Bishop tells Arthur that before they get their freedom they must do one last mission, ride north through the Woads territory towards the invading Saxons (who kill everyone in their path) rescue the Pope's godson and his parents since the Romans are withdrawing forces from Britannia. Arthur is heartbroken that he must disappoint his men and tell them of one more mission. They leave the next day.
They get ambushed by Woads, but Merlin spares them. They make their way to the home of the godson. Immediately Arthur hates the father for being so brutal to his serfs. Dagonet breaks down a wall & door in a side hut where we find that the father has had pagans chained up and starved to death for being pagan. Dagonet finds a little boy and Arthur finds a young woman. Outside they hear the drums of the Saxons (one group coming from the North while another comes from the South), Arthur orders everyone to go through the mountains (three to four dozen people). During the trip we find out that the woman is Guinevere and that she is a Woad.
During the journey, the group has to cross a frozen lake, they can hear the ice craking but that is soon drowned out by the drums of the Saxons. Arthur orders everyone back to Hadriam's Wall. Arthur, his knights, and Guinevere all stand with bows. The infintry Saxons advance, they shoot their arrows to see if the small group is within range, they aren't. Then Arthur orders Tristian and Bors to fire and they kill 4. The Saxons advance, Arthur orders everyone to shoot for the sides to make them cluster which they do immediately, the ice starts to crack more but not enough to break. Arthur orders them back to stand and fight when Dagonet grabs his axe and runs to the middle between the two groups and swings his axe several times into the ice to get it to break (from the trailer). He is shot with arrows and Arthur runs after him with Bors behind. The ice breaks swallowing dozens of Saxons. Arthur wins.
Back at the Wall, the bishop gives the knights their papers and they are free. That night Arthur is called to the top of the wall to find Saxons in front of him. Arthur and Guinevere make love that night (no love traingle).
The next day, Arthur is alone on a hill while the other knights ride off with the peasants who are fleeing. Arthur meets with main bad guy, Cerdic, and returns. When he goes back, Lancelot and the others ride to his side (there are only 6 of them). In the bushes we see Guinevere (boob belt and all) with the woads. Small group of Saxons enter the gate, which closes behind them shielding them from view of the rest of their army. (The best battle seen I've seen in a while) The Woads attack them with arrows while Arthur and his 5 knights ride through their ranks killing then disappearing through the smoke, this is repeated 2-3 more times till all of those Saxons are dead.
Gate opens again, all the Saxons enter this time. Cerdic sends his son, Cynric, and a group in one direction while he leads the others in the other direction. The Woads fire arrows that are aflame igniting the oil on the groud seperating the two halves. Battle is brief as far as movies go. Guinevere fights Cynric, Lancelot sees that she's not doing good (and he knows that Arthur loves her) and goes to step in, kicks Cynric's butt knocking him to the ground but is distracted long enough for Cynric to grab nearby bow and arrow. Lancelot is shot in the heart, but throws one of his swords into Cynric's chest killing him first, Lancelot dies!
Meanwhile, Tristain and Cerdic are fighting. Tristian eventually loses. He dies too. Arthur finally gets to Cerdic, they fight, Cerdic gets the upperhand on a kneeling Arthur for about 2 seconds but Arthur wastes no time in stabbing him from behind!