The kingdom of Rheged has been found following excavation work by Gatehouse of Fleet in Dumfries and Galloway.
Previously, it was thought the kingdom was headquartered in Cumbria although no evidence of it was ever found.
Archaeologists were first drawn to the site by Pictish carvings in stones at Trusty’s Hill given the unusual southerly location of the markings.
But the team from GUARD Archaeology now believe the carvings belong to the stronghold of King Urien’s where inauguration ceremonies for the Britons of Galloway were held around 600AD.
Ronan Toolis, who led the excavation, said: “The new archaeological evidence suggests that Galloway may have been the heart of the lost Dark Age kingdom of Rheged, a kingdom that was in the late sixth century pre-eminent amongst the kingdoms of the north.”
Excavations have revealed the summit of the hill was fortified with a timber-laced stone rampart.
A symbolic entrance way, with two Pictish symbols marked on one side, is believed to have led to the fort where rituals of royal inauguration were conducted.
Archaeologists have built up a vivid picture of life at the fort given their findings.
The excavation found the remains of a workshop that was producing high status metalwork of gold, silver, bronze and iron.
Other activities apparent at Trusty’s Hill included the spinning of wool, preparation of leather and feasting.
Diet of this early medieval household was predominantly cattle, oats and barley.
Dr Christopher Bowles, co-director of the excavation, added: “This household is likely to have been connected with an international trade network that linked important sites around the Irish Sea with Continental Europe.
“The power of this royal household was maintained by bonding the people of this land and the districts beyond by gifts, promises of protection and the bounties of raiding and warfare.”
The finds have been made as part of the Galloway Picts Project which was launched in 2012.
New analysis of the symbols have confirmed the symbols are genuine early medieval carvings, likely created by a local Briton blending innovation with deep seated traditions.
Mr Toolis added: “The literal meaning of the symbols at Trusty’s Hill will probably never be known.
“There is no Pictish Rosetta Stone. But these symbols and the material culture we recovered provide significant evidence for the initial cross cultural exchanges that forged the notion of kingship in early medieval Scotland.”
The Lost Dark Age Kingdom of Rheged by Ronan Toolis and Christopher Bowles is published by Oxbow Books .