A long lost Roman emperor, who took control of an isolated outpost when Rome descended into a chaotic civil war, has been discovered.
Coins depicting the emperor Sponsian were unearthed in a horde in Transylvania in 1713, but because no historical records exist of the leader, they were assumed to be forgeries.
Now, new microscopic analysis shows they bear the same wear-and-tear as genuine coins, suggesting they must have been recognised and used as currency.
Experts now believe Sponsian was a Roman general in the imperial Province of Dacia - Transylvania, in modern Romania - which was prized for its gold mines but cut off from the rest of the Roman empire in around 260 AD.
Surrounded by enemies, Sponsian may have been forced to assume supreme command to protect the military and civilian population of Dacia until order was restored, and the province evacuated between 271 and 275 AD.
To pay the legions and assert his authority, he minted gold coins bearing his image, and inscribed them with the legend “IMP Sponsiani”, meaning “belonging to the Imperator (emperor) Sponsian”.
Paul Pearson, of University College London, said: “His coins are very deeply worn and so appear to have been in circulation for an appreciable period, and yet they are only known from Transylvania,” he told The Telegraph.
“The best time window that explains this is the decade or so between the early 260s and early 270s when the Province of Dacia was cut off from the imperial centre.
“With no pay coming in from Rome because of civil war and instability on the borderlands, economic collapse and mutiny would have been major risks.
“We think the administration chose to mint crude gold coins to pay the senior soldiers and officials which could have been traded down for the regular pre-crisis coinage that was circulating in the area.”
Sponsian seems to have taken command during the reign of Gallienus, who ruled Rome between 260 and 268AD. At its peak, the garrison at Dacia stood 50,000 strong, but by the mid-third century it was surrounded by hostile groups such as the Goths, the Carpi and the Sarmatians.
At the time, the Roman empire was split into three chunks and Dacia and the provinces south of the Danube had been devastated and depopulated by foreign invasions, leaving Sponsian and his soldiers cut off.
The experts say that although he styled himself as an emperor, there is no evidence he aspired to conquer more lands, or rule the empire as a whole.
In the 270s, when order was finally restored in the area by the Emperor Aurelian, the province of Dacia merged seamlessly back into Imperial Rome without the need to be conquered.
Only four coins featuring Sponsian are known to have survived to the present day, with one in The Hunterian collection at the University of Glasgow.
Curator of Numismatics at The Hunterian, Jesper Ericsson, said: “This has been a really exciting project for The Hunterian and we’re delighted that our findings have inspired collaborative research with museum colleagues in Romania.
“Not only do we hope that this encourages further debate about Sponsian as a historical figure, but also the investigation of coins relating to him held in other museums across Europe.”
The coins, which are believed to be priceless, are now on public display at The Hunterian.