L EGEND has it that King Arthur and his knights will return in Britain’s hour of greatest need.

Brave and true of heart, they will ride out from their place of slumber – a cavern in the depths of Sewingshields Crags – and across the Roman lands of Tynedale that will probably have changed little since Arthur’s final battle with Mordred, 1500 years ago.

The fabled leader, of medieval history and romance, is reputed to have defended Britain from those scary Saxon invaders and is said, to this day, to be on standby, ready to unsheathe his sword once again.

But how did this Cornish King, supposedly conceived at Tintagel, ever come to be associated with these far-flung borderlands?

Because as the trusty Ordnance Survey map of Hadrian’s Wall seems to show, he made his mark.

If you run your finger northwards from Haydon Bridge, over the thin line representing the Military Road and onward, over the Whin Sill ridge that supported Hadrian’s Wall, you drop down on to the Fozy Moss area of marshland where Sewingshields Castle once stood.

In truth it was probably no more than a simple tower house (the last owner was Sir Robert Ogle, who died in 1437) but interest in it has been peaked by its near bedfellows. Just some of the names dotted across the landscape are King’s Crags, Queen’s Crags – in honour of Guinevere, it is said – King Arthur’s Well and King Arthur’s Chair.

One popular yarn has it that during the 1800s, a shepherd was sitting knitting near the overgrown ruins of Sewingshields Castle, when he dropped his ball of wool. Running after it, he stumbled upon a hidden passageway and followed it.

At the end was a grand subterranean hall, with a huge table in the centre – around which were sat King Arthur, Guinevere and the Knights of the Round Table. They were all in a deep slumber.

On the table lay a bugle, a garter and the sword Excalibur. Acting on instinct, the shepherd picked up Excalibur and cut the garter, upon which moment Arthur and company awoke.

Startled, the shepherd hastily returned the sword to its sheath, prompting Arthur to mutter in anger: “O, woe betide the evil day On which this witless wight was born, Who drew the sword, the garter cut, But never blew the bugle horn.”

The Arthurian entourage went back to sleep. However, the fleeing shepherd took with him the knowledge that help for Britannia was but a bugle call away.

Durham University professor Elizabeth Archibald, who owns the farm in the North Tyne Valley where Tarset Castle once stood, has more ability than most to separate fact from fantasy.

The holder of a PhD in medieval studies from Yale, with special interest in Arthurian legend, she yet says: “Arthur’s origins, and his historicity, are shrouded in mystery and we will probably never know whether he really existed.

“If he really was an early British ruler or war leader, it would have been in the fifth or sixth century, just after the Romans abandoned Britain, a time for which we have very few reliable records.”

According to one school of thought, he was an historical figure who had been turned into a legendary hero in a world of supernatural adventure; but according to another, it was just the opposite – he was a protective deity who had been turned into an ‘historical’ character.

The co-editor of The Cambridge Companion to the Arthurian Legend , she said: “As a scholar of medieval literature, I don’t really care which of these theories is true.

“What interests me is what sort of stories have been told about him through the ages, what social attitudes and concerns they reveal, and why his legend has enjoyed such evergreen popularity for over a thousand years.”

It seemed surprising that Shakespeare hadn’t written an Arthurian play, drawing on the powerful mixture of family and political tensions and crises in the story, with its clandestine love affair between the king’s wife and his best knight, and the ultimate betrayal of father by son.

But it seemed the legend had gone out of fashion by his era and didn’t find favour again until the 19th century, when Sir Walter Scott revived interest in the Middle Ages.

Arthurian themes had inspired many a Pre-Raphaelite painting, as well as Alfred Lord Tennyson’s influential series of poems, Idylls of the King . And Arthur had certainly lived on in the popular imagination today – films, graphic novels and television series paid testimony to that.

Despite the bank of research and ‘historical’ records built up over the centuries, though, one of the greatest mysteries about King Arthur was where he might have lived. The earliest references to him were tantalizingly brief.

There were many places in England and beyond where Arthur, the once and future king, was supposed to be sleeping in a cave with his knights, waiting till England needed them again.

Sewingshields was just one such place, Mount Etna in Sicily another. Prof. Archibald said: “He is often associated with a great victory over the invading Saxons at Mount Badon, but there is considerable debate about the site of this battle, and in a description of it written a generation after the event by a reliable commentator, Arthur is not mentioned.

“Some scholars therefore argue that if he existed, he lived not in the south, where the battle of Badon took place, but in the north of England or southern Scotland.

“His story may not have been known in the south at all until Britons fleeing the Anglo-Saxon invaders migrated down to Wales; it’s easy to imagine that within a few generations, the legend was relocated to Wales, and perhaps Cornwall too.”

Several Scottish kings had called their sons Arthur in the sixth century, at a time when it was otherwise an unusual name.

King Arthur is supposed to have died at the battle of Camlann, a name linked with the Roman fort of Camboglanna on Hadrian’s Wall. Counting from the East, that was the twelfth fort on the Wall, located seven miles west of the one at Birdoswald.

That would account for Arthur’s absence from early southern records – and for the story that he is biding his time at Sewingshields, under the windswept crags of England’s most northerly frontier.