McArthur says the legend is based on Arthur, a sixth-century war-band leader that ruled over Strathclyde, a kingdom of Welsh-speaking Britons that stretched from Loch Lomond in Scotland down to north Wales. The kingdom's capital was Dumbarton in west-central Scotland.
"There's a large number of place-names in the region which can be linked to Arthur," he said. "At Dumbarton itself there's Arthur's Castle, and just to the west of Loch Lomond, there's a mountain called Ben Arthur, which includes a site known as Arthur's Seat."
McArthur says it's just one of seven "Arthur's Seats" he has uncovered in Scotland.
"There are 40 to 50 place-names in Scotland with the name of Arthur in them," he added. "I can't say they are all Arthurian, but there's an awful lot of them that are."
And he says the most likely location for Avalon (the holy island where Arthur received his sword Excalibur and was later taken when mortally wounded) is on Loch Lomond. Historians believe Arthur's main battleschronicled by Nennius, a ninth-century Welsh monkwere fought nearby.
McArthur, who claims his clan is directly descended from the Strathclyde Arthur, says the king's bloody struggles to convert pagan tribes were later airbrushed out of accounts of the Christianization of Scotland. "Christians didn't want to write themselves up as a bloodthirsty crew," he explained.
"Another problem was that Strathclyde was a Welsh-speaking nation," he added. "As the language retreated into modern-day Wales and Cornwall, the story went with them."
McArthur's theory has support from Edinburgh-based Scottish historian Stuart McHardy, author of The Quest for Arthur.
Though McHardy believes Arthurian legend is probably largely mythological, he added, "There's a very good argument for saying there was an historical character in the sixth century. He was leading a Christian crusade against the pagans in the bottom half of Scotland, which is the best match for all the battles mentioned by Nennius."
He says Guinevere is buried in Meigle, Perthshire. "And Merlin is thought to be buried not that far from here," he added.
As for Arthur being part of the Roman occupying force in northern England, as portrayed in the new movie, McHardy said, "The Roman connection is complete rubbish as far as I'm concerned."
The Romans left Britain at the start of the fifth centuryabout a hundred years before Arthur is said to have led a resistance campaign against invading Germanic tribes.
For instance, ancient accounts refer to a major battle at Badon Hill, an unknown location where Arthur's forces defeated the Anglo-Saxons in around A.D. 500. Like McArthur, McHardy thinks stories associated with King Arthur filtered south as Welsh-speaking Britons were gradually pushed out of Scotland by the Picts. These stories were then interwoven with local English landmarks.
"They were set within the known environment, so that people could absorb them," he said.
Tintagel, an ancient castle on the north coast of Cornwall, is perhaps the most familiar Arthurian setting. It's been claimed as Arthur's birthplace since medieval times.
Likewise, Glastonbury, in Somerset, has long been associated with Avalon. Similar historic sites are promoted by tourism offices around the country.
Given the mythology surrounding Arthur, and the difficulty in pinning him down historically, it's not surprising so many places now claim him as their own.
Indeed, the legend is multinational these days, with Arthur's origins linked to countries including France, Iceland, Italy, Norway, and Hungary. Given Arthur's ability to cross national borders so readily, maybe it doesn't really matter who Arthur was or where he came from.
"Stories exist where they are told and are as relevant in that place as any other," McHardy concedes.
So the story is in the telling, even if the latest one does come from Hollywood.
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