Under the Crosskeys Bridge in Lincolnshire, England, farmland stretches flat and green and the River Nene lies brown and shallow. When the North Sea tide rises, 6km away, it flows upriver as fast as a human runner. Around the time of the full and new moons, the water can outrun a galloping horse as it races across the low, flat landscape.

Somewhere near here in 1216, ‘Bad King John’ – a monarch so incompetent and evil that his name is still preserved in folklore, films and nursery rhymes – was running from his enemies. When his army tried to cross the mudscapes of the tidal estuary that Britons call the Wash, rising waters caught his baggage train. The wagons and their contents, including the king’s treasure, were lost.

More than 800 years later, King John’s hoard has not been found. But it still lures believers. And one local man thinks he has found its location.

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Edward Morris knows the marsh and its dangers well. (Because of a contractual obligation with the company that owns the land where he believes the treasure lies, he can’t use his real name in the press; his first name in this story has been changed). He found his first clue more than seven years ago while metal detecting with his son. “All of a sudden, we got this massive signal: the machine started beeping really loud, and we started to dig,” he recalled. “We must have dug down about four feet from the side of a dyke… and I retrieved an object about the size of a golf ball and covered in rust.”

Morris didn’t look closely at the object again for three months. But then, he said, he met a tarot card reader who identified his dead mother at his shoulder – and reminded Morris of his own childhood fall through an abandoned mill. She added something else that drew him back to his find.

“She basically said that what I’m looking for is magnificent, out of this world, but until I work the puzzle out I won’t know what I’m looking for,” Morris said. He felt a mysterious pull to the drawer where the object lay untouched and covered in rust, and his journey into obsession began.

What I’m looking for is magnificent, out of this world

When it comes to tracking down King John’s treasure, methods both scientific and supernatural have proved equally unsuccessful. During the 1930s, a wealthy American founded the Fen Research Company to search for the treasure, using what were then cutting-edge techniques. More recently, London barrister Walton Hornsby hired a dowser, or traditional diviner, to solve the mystery. He, too, came up empty-handed.

Despite the various attempts at recovery, no-one can be sure exactly what the hoard contained. One chronicler describes the loss as a catastrophe on the scale of the Titanic. Another simply says the king lost part of his chapel and ornaments. There is, however, strong circumstantial evidence that John lost at least one crown.

Best known for his role as the eternal bad guy in the tale of Robin Hood, King John was not associated with the merry men until centuries after his death. But even in an era when a peasant could lose both his sight and his genitals for hunting deer in the royal forest, he was infamous for his cruelty. He had such a knack for making enemies that he provoked medieval warrior oligarchs into drafting the founding document of English democracy, the Magna Carta, and managed to lose most of modern France and much of modern England.

Historian Marc Morris (no relation to Edward) has written a biography of the monarch. Was the king as bad as he is made out to be? “Oh no,” Morris said gleefully. “Much worse. In legend, he doesn’t starve people to death. In reality, he does – en masse.”

While generations of English schoolchildren learned about King John simply as ‘Bad King John’, the monarch’s name is preserved a little more sympathetically in the lands around the Wash. A King John’s Bank rises above the flatlands not far from the Crosskeys Bridge. In the prosperous market town of King’s Lynn, from which John set out on his fateful journey, a gaol-turned-museum holds what is proudly (and erroneously) described as the King John Cup, and King John Avenue bears his name.

Today, the marsh itself remains a treacherous mass of mud, quicksand and hidden streams, not dissimilar to the mire that entrapped the baggage carts so many centuries ago. But land reclamation efforts spanning more than five centuries have transformed the landscape around the Wash, taming the estuary and redefining the area it describes. While mud flats still shimmer to the horizon, salt marshes are now farmland and waterways once dug for drainage now wind their way metres above the potato fields: boats, surreally, sometimes float high above one’s head.

Morris thinks that some of the more recent changes helped lead to his discovery. He believes the little metal piece he found seven years ago is part of the clasp of a box – and that the box from which it was knocked, perhaps by someone ploughing a field a century ago, is still intact.

Morris, who left school before he turned 16, researches maps and data independently, finding and unpicking clues in the manner of a Dan Brown hero. In the little market town of Long Sutton, 5km or so from Crosskeys Bridge, King John once issued a charter giving permission for a fair. The town’s Church of St Mary dates back in places to around that time, and its stained-glass window includes a quatrefoil – a shape like a four-leafed clover. On the piece Morris found, blobs of different-coloured metals form a similar outline against a circular background. He sees this as a sign that his object, like the church, has royal connections.

All of Morris’s research points back to the field where he found his original clue. There he believes he can see the outline of 21 sunken carriages on Google Earth. But neither the tenant farmer who leases the field nor the company that owns the land have wanted to give Morris permission to dig without a geophysical survey indicating there was something to be found.

And so, a year or so ago, Morris created the character of Metal Detector Man to help fund the £10,000 cost of the survey and attract attention to his cause. Besides appearing at local shows and events, he began to craft junk he found while detecting into pieces of art, hoping to raise both money and his profile: so far, he has secured a little over £1,000.

Faced with these odds, most people would have given up on this quest long ago. But one clue, in particular, has kept Morris motivated.

The code “F8199” is inscribed on the object he found. Over weeks of frantic Googling, Morris could not find a match for F8199 and the name King John. Then Morris’s partner, with whom he has lived since they were teenagers, suggested the number might be linked to one of John’s ancestors. A search for “F8199” and “Matilda” pulled up the family tree of a countess named Mathilda.

“What I’d found is a royal family information number for royalty,” Morris said. “When they made things for their purposes, like boxes, trunks, all that sort of stuff, the makers would have put their marks on it or their royal information number on it.”

Historians would say that interpretation is based on a fallacy. Royal families of that period did not watermark their possessions; F8199 is a code assigned by modern genealogists to a specific family group, not a reference from the medieval era; and this ‘Mathilda’ is not the medieval claimant to the English throne but an earlier, more obscure Matilda. But for Morris, it was a eureka moment that encouraged him to press on with his quest.

Since finding the object, Morris has been caught in a push-and-pull between the obsession with treasure and a desire just to be free of it, to put his quest aside. “The more I researched, everything pulled into John,” he said. “If it didn’t, I wouldn’t have bothered.” He has even seen the dead king’s face staring back at him from his bathroom mirror, he said.

Backed by the shimmering mudflats of the Wash, Morris gathered samphire, a local succulent that’s a seasonal delicacy, and inspected the object that has become his defining passion. He has embedded it into a piece of art, a beautiful polished bowl carved from a piece of driftwood. The aim was, initially, to free him from his obsession – yet the work now serves to promote it.

A perfect circle of brass with blobs of solder in the centre, Morris’s find could once have been part of a clasp, a lock or even a machine. But it did not, at first blush, look 800 years old. The code appears machine-cut; the numerals are Arabic, not Roman.

The historian Morris was sceptical of the treasure hunter’s evidence. “The chances of carriages surviving for more than a few generations are remote,” he said. “Once you get wood into water, it perishes by and large. The chances of seeing them from Google Earth? You’ve probably got a better chance of seeing Elvis down Waitrose.”

“My advice would be: if you think you have found a piece of treasure that relates to the royals in the 11th, 12th or 13th Century, take it to the British Museum or take it to your local county archaeologist. Have them assess it – and let them give you their expert opinion,” he added.

Yet even if Edward Morris pursued that option, it’s not clear that would bring an end to his quest. As for so many treasure seekers before him, it will take more than an expert opinion to quench his thirst for discovery.

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