This is the movie that claims to be historically accurate.  It’s based on the Arthur proposed as the origin of the legends by Linda Malcor and Scott Littleton, in their book From Scythia to Camelot.  Briefly, Malcor and Littleton argue that the  original Arthur was Lucius Artorius Castus, a Roman commander in charge of 5500 heavily-armored Scythian auxiliary cavalry, stationed on Hadrian’s Wall (the border between the province of Britannia and the land of the Picts, now Scotland) in the third century.  There are strong similarities between the mythology of the Sarmatians and some elements in the Arthurian legend, and so Littleton and Malcor proposed that Lucius Artorius Castus was the original King Arthur.

It's actually difficult to imagine on what level this movie succeeds. Inconsistencies abound--Arthur fights the Saxons on a frozen lake, and in the next scene, it's full summer with an oak tree in full leaf. Hadrian's Wall is fully manned by Roman soldiers, even though they had been gone from Britain for over forty years at the time the movie takes place. Above all, the teenaged Guinevere just doesn't have the authority to lecture the forty-something veteran of many wars Arthur on pacifism. It just doesn't work.