A PLASTIC injection moulder from Chipping Norton has discovered proof of a hitherto unknown 3rd-century Caesar in the mud of an Oxfordshire field.

Experts at the British Museum have confirmed that a coin bearing the profile of a striking bearded man which was unearthed by Brian Malin and his metal detector as part of a buried hoard proves the existence of the Roman Emperor Domitianus. The find will require the history of one of the Roman Empire’s murkier periods to be rewritten.

It is almost as though an amateur had suddenly discovered evidence of a previously unknown British king sitting briefly on the throne between the reigns of George I and George II.

Historians knew of a high-ranking army officer named Domitianus who appears in a couple of fleeting references of the period. But they knew of no emperor of that name, and they are still uncertain whe-ther the man who appears on the rare coin the size of a 20p piece is that same officer, or an entirely different figure with the same name.

Either way, classicists are thrilled. Richard Abdy, curator of Roman coins at the British Museum, said yesterday: “This find rewrites history; it is the final piece in a jigsaw. Only the archaeological evidence of this coin shows that he was indeed emperor and provides us with a face to go with history’s forgotten ruler.”

As well as the name of Domitianus, the coin bears the Latin abbreviations for “Imperial” and “Caesar”.

The find, discovered 2ft below ground on farmland ten miles from Oxford, also confirms the authenticity of a coin which was dismissed as a hoax when it was found in 1900 in the Loire region of France because it was unique and unprecedented.

The Oxfordshire example now vindicates it: its antiquity is beyond doubt as it was among more than 5,000 common Roman coins fused together in a 3rd-century AD pot that had to be painstakingly separated by British Museum conservators. It is unusual to find such treasure intact rather than dented or scattered by the plough.

Mr Malin was on one of his regular days out with his metal detector, a passion since he was 15. Until now he had never found more than the occasional Roman coin.

As the hoard emerged from clumps of earth, he knew he had found something special: “I was amazed when I dug the pot out. It took me by complete surprise,” he said.

Most of the coins are common, just like of hundreds of thousands of others. That only heightened the excitement of finding the Domitianus example among them. At the British Museum, Mr Abdy said the find was as unexpected as flicking through a pack of cards and coming across an 11 of clubs. “We ran to the Who’s Who of later known emperors.

“The new discovery makes it certain both that this shadowy claimant to the Imperial throne existed, and that he mounted a serious challenge for the position of emperor in the troubled period of the early 270s AD, known as the Gallic Empire.”

The Gallic Empire is the name given to the secessionist state that was created in AD260 in the aftermath of the Roman Empire’s greatest humiliation. It spanned Gaul — modern France and the Rhineland — and Britain, and survived as a separate state for almost 15 years before being reabsorbed into the central Roman Empire by Aurelian.

It was established after the Emperor Valerian was captured alive by the Persians and used by the Persian King, Sapor, as a living footstool for mounting his horse. On his death, having had his eyes gouged out, Valerian was stuffed and displayed in a Zoroastrian temple.

Mr Abdy said: “This was the cue for Gaul to revolt in order to look after their own security, taking Britain and initially the Iberian Peninsula with it.

“An officer called Postumus became the first breakaway Gallic ‘emperor’ with his capital in Trier. This is the probable location for the minting of the Domitianus coin. AD269 was a particularly turbulent year for the Gallic empire, with three successors to Postumus staking rival claims. Finally power settled on Victorinus, who was reportedly prone to raping the wives of his courtiers. In 271, he was killed after propositioning the wife of one of his officials. Domitianus may have been one of the wronged husbands. Striking coins was a sign of seizing the purple.

Domitianus may only have ruled for days, weeks or months, scholars suggest, before he was overthrown by Tetricus, the Governor of Aquitaine, emperor from AD271-74.

The coin will go on public display from today until March 14 in the British Museum Buried Treasure: Finding Our Past exhibition.

A coroner will then decide whether to declare it treasure, and an independent body of experts will establish its value. A five-figure sum is expected to be paid to the finder.

The Ashmolean Museum in Oxford has already expressed interest in acquiring it for its new “money gallery”.

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