The stories of a chivalrous royal court, Merlin the wizard, and a magical sword - first found in Geoffrey of Monmouth's History of the Kings of Britain, written in 1139 - have generally been seen as an entertaining fantasy.
But according to John Gillingham, a medieval historian at the London School of Economics, they were written to stifle the idea that the Welsh were uncouth and had a worthless culture.
His research, published in the journal Anglo-Norman Studies, found that Geoffrey, a Welshman, wrote his saga at a time when the Welsh began to suffer English contempt for the first time.
Before the early 12th century, he says, the English had viewed the Welsh, Scots and Irish as 'Christians like themselves', even though they were often at war with one another. But from around 1125, they began to write about the Celts as barbarians.
Geoffrey's work, he explains, should be seen as a response to that growing contempt. In the first history of the pro-Saxon Britons (or Welsh), King Arthur's lineage was traced to Aeneas of Troy, the mythical founder of Rome. His forebears were depicted as town-builders and law-givers - gentle knights not savages.
English contempt for the 12th century Welsh and Scots was partly understandable, the study found. The Celts were as backward, economically and socially, as the English had been in the eighth century.
From 1136-8 a 'great revolt' in Wales had defeated the English armies twice and retrieved much of the country from English hands. Geoffrey intended King Arthur to be identified with the leaders of that revolt, Mr Gillingham said.
The legend had no long-term success as pro-Welsh propaganda, however. It was rewritten and embellished by later Anglo-Norman writers.Reuse content