Arthur, also known as Artorius Castus (Clive Owen), is portrayed as a Roman cavalry officer and commander, the son of a Roman father and a Celtic mother, who leads a military force of Sarmatian cavalry in Britain at the close of the Roman occupation in 467 A.D. He and his men guard Hadrian's Wall against the "Woads", a Celtic people who resist Roman rule, based on the historical Picts, led by their mysterious leader Merlin. He is not the first Arthur - over the years, many of his ancestors have thrown the Wall, leading Sarmatian auxiliaries.
As the film starts, Arthur and his remaining men Lancelot (whose voiceover is heard at the beginning and end), Bors, Tristan, Gawain, Galahad and Dagonet - are expecting discharge from the service of the Empire after faithfully serving for 15 years (Lancelot's entry into service as a youth in 452 A.D. is depicted at the very beginning of the film). However, they are dispatched on a final and possibly suicidal mission by Bishop G