The Salisbury Magna Carta, one of the original surviving Magna Carta manuscripts. An additional one was just found in Sandwich, England. (Alastair Grant/AP)

Sometimes, the most stunning discoveries aren’t buried under feet of earth or stashed in a cave, but hiding in plain view. They’re tucked away in some musty archive — discovered, documented, but somehow lost.

Such was the case on a recent day in the British coastal town of Sandwich. That’s where an ancient copy of the Magna Carta — a document that in part inspired the U.S. Constitution and serves as a foundation of modern democracy — just turned up in a scrapbook.

At the end of December, an organization called the Magna Carta Research Project asked a small-town historian named Mark Bateson to look up a local copy of the Charter of the Forest, a British document that made land available to commoners in the 12th century and is considered a companion to the Magna Carta. In doing so, the historian came upon a tattered parchment about three feet long. It was rotten and soggy from centuries of neglect — but clearly a Magna Carta issued in 1300 by royal decree.

“It had survived, unbeknownst to its archivists, in a scrapbook compiled by a British Museum official at the end of the 19th century,” the Magna Carta Research Project said in a statement.

The news, which comes on the heels of a major gathering of Magna Carta manuscripts, was a big deal for a number of reasons. For one, the manuscript was found with the Charter of the Forest for just the second time in history. Then there’s the fact of its age. King John oversaw the original Magna Carta, a fundamental pillar of human rights, in 1215. To date, only seven known copies of the 1300 Magna Carta are known to exist.

The only four surviving copies of Britian's 800-year-old Magna Carta are together for the first time as part of an exhibit at the British Library in London. (Reuters)

The document has a staggering value: $15 million.

“It is a fantastic discovery which comes in the week that the four other known versions were brought together at the Houses of Parliament,” Nicholas Vincent of the University of East Anglia, who authenticated the find, told the Press Association. “It’s a fantastic piece of news for Sandwich which puts it in a small category of towns and institutions that own a 1300 issue. … It must have been much more widely distributed than previously thought because if Sandwich had one … the chances are it went out to a lot of other towns. And it is very likely that there are one or two out there somewhere that no one has spotted yet.”

The document doesn’t look that great after more than 700 years, however. In fact, it looks like a rag that sopped up some paint, with about one-third missing. It’s also missing its royal seal, which each copy of the 1300 Magna Carta — the final iteration the crown distributed — carried.

Despite the document’s value, local authorities aren’t planning on cashing in. Sandwich hopes it will be a tourist attraction.

“We are absolutely delighted to discover that an original Magna Carta and the original Charter of the Forest, previously unknown, are in our ownership,” said Paul Graeme, mayor of Sandwich town council. “To own one of these documents, let alone both, is an immense privilege given their international importance.”