A hoard of gold coins once thought to be fakes have been authenticated by researchers who say the artefacts reveal a long-lost Roman emperor.

The coins bear the name and image of a shadowy historical figure, Sponsian, whose existence was previously placed in doubt by experts who suggested the coins were the work of sophisticated 18th-century fraudsters.

But a scientific analysis has concluded that the coins are genuine third-century artefacts, and the researchers make the case that Emperor Sponsian was also the real deal.

“We’re very confident that they’re authentic,” said Prof Paul Pearson, of University College London, who led the research. “Our evidence suggests Sponsian ruled Roman Dacia, an isolated goldmining outpost, at a time when the empire was beset by civil wars and the borderlands were overrun by plundering invaders.”

The hoard of coins are said to have been unearthed in Transylvania, in modern-day Romania, in 1713. Several depict recognised Roman emperors of the third century, including Gordian III and Philip the Arab. But four coins bear the name and image of Sponsian, who does not appear in any other historical records.

When the coins were discovered, they were initially thought to be genuine. But from the mid-19th century, attitudes changed owing to the coins’ crude designs and jumbled inscriptions. One expert suggested they were the work of a sophisticated Viennese fraudster who had invented an emperor to appeal to collectors, and this became the prevailing view.

Pearson, an earth scientist, learned about the coins and the “fake emperor” while researching a book on Roman history as a lockdown project. He began corresponding with Jesper Ericsson, the numismatics curator at the Hunterian museum in Glasgow, which holds a coin in its collection, and the pair decided to perform a full scientific analysis.

This revealed that simply based on their weight in gold, the coins are valuable – the assemblage would be worth $20,000 (£16,700) in modern value. “If they’re a forgery, that’s a big outlay to start with,” said Pearson.

When examined at high magnification using optical imaging and electron microscopy, the coins showed similar patterns of wear and tear to genuine coins, suggesting they had been in circulation for several years. Minerals on the surface of the coins were consistent with them having been buried for an extended period, and the scientists detected sulphate crystals, which typically form when an object is deprived of oxygen for a long time and then re-exposed to air.

“I believe we have established with a very high degree of confidence that they are genuine,” said Pearson, adding that the question of Sponsian’s identity was “more speculative”.

It is known that the Dacia region was cut off from central command during a period of military strife in the 260s CE. Writing in the journal Plos One, the authors speculate that Sponsian was a military leader who assumed authority over the Roman enclave and established a local coin mint.

“He took on the title imperator – supreme military commander – that was reserved for the emperor,” said Pearson. “There are other precedents of regional emperors. If we allow Roman emperors to self-identify, he was a Roman emperor.”

Dr Adrastos Omissi, of the University of Glasgow, who was not involved in the research, described the analysis as “a brilliant piece of work”. “I think they’ve made a really convincing argument for the existence of Sponsian and of him being a real emperor,” he said, adding that the late 3rd century was a period of such turbulence and unrest that “the bar for being an emperor was very low”.

However, others were more sceptical. “They’ve gone full fantasy,” said Richard Abdy, the curator of Roman and iron age coins at the British Museum. “It’s circular evidence. They’re saying because of the coin there’s the person, and the person therefore must have made the coin.”