Britain's Dark Ages were not so dark, the National Trust has revealed, after archaeologists discovered an intricate mosaic built long after the Romans left.
It was widely thought that when imperial troops withdrew in 410 AD they took civilisation with them and a benighted Britain fell into subsistence farming and warring factions.
But archaeologists at Chedworth Roman Villa in Gloucestershire have used buried bone to radiocarbon date a sophisticated floor mosaic to at least 428 AD - long after Roman rule ended.
The first known 5th century mosaic in the UK shows that native Britons continued to enjoy a high level of craftsmanship, wealth, and luxury for far longer than previously thought.
Results had to be checked twice as they contradict the long-held story of rapid decline between 400 years of Roman control and the Anglo-Saxon settlement, when lavish villas were assumed to have been left abandoned.
Martin Papworth, an archaeologist with the National Trust, said: "The 5th century is a time which marks the beginning of the sub-Roman period, often called the Dark Ages. After almost 400 years, Britain had been lost by Rome. This saw production decline, and the craft and service industries became unsustainable. It has generally been believed that most of the population turned to subsistence farming to sustain themselves.
"Britannia's administrative system broke down into a series of local fiefdoms. What is so exciting about the dating of this mosaic... is that it is evidence for a more gradual decline."
Chedworth Villa is one of the largest and best preserved Roman villas in the country, and experts working at the site since 2012 used charcoal and bone fragments unearthed in the foundation to date one of its 35 rooms.
This recently completed dating revealed the room was a new addition built after Imperial rule in 428, but displayed an intricate mosaic of braided and floral patterns which was not expected of the Dark Ages.
"The creation of a new room and the laying of a new floor suggests wealth, and a mosaic industry continuing 50 years later than had been expected," Mr Papworth said.
"I am still reeling from the shock of this dating," said Dr Stephen Cosh, an expert on Roman mosaics.
"There is no question that this find at Chedworth is of enormous significance. It's tremendously exciting."