Archaeologists may have finally found the lost kingdom of Rheged, the most elusive of all the sixth century kingdoms of Dark Age Britain.

The mysterious kingdom was pre-eminent in northern Britain in the sixth century, but faded into obscurity after it was deliberately destroyed in the beginning of the following century.

Historians had speculated that the kingdom was headquartered in Cumbria, a county in north west England, but no evidence of it was ever found. Then digs carried in 2012 at Trusty's Hill, which overlooks the Fleet valley in Galloway in south-west Scotland, revealed clues of the presence of a royal stronghold.

"Our excavation revealed all the hallmarks of an early medieval royal site," Ronan Toolis at GUARD Archaeology in Glasgow, told Seeker.

The discovery is detailed in a new book, "The Lost Dark Age Kingdom of Rheged," which is being released Saturday.

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Toolis and co-author Christopher Bowles found that in the decades around 600 A.D. the summit of the hill was fortified with a timber-laced stone rampart. They also recovered remains of supplementary defenses and enclosures along the lower-lying slopes, revealing that Trusty's Hill was fortified.

"This is a type of fort that has been recognized in Scotland as a form of high status secular settlement of the early medieval period," Toolis said. "The evidence makes a compelling case for Galloway being the core of the kingdom of Rheged."