Bought for $27.50 after World War II, the faint, water stained manuscript in the library of Harvard Law School had attracted relatively little attention since it arrived there in 1946.

That is about to change.

Two British academics, one of whom happened on the manuscript by chance, have discovered that it is an original 1300 version — not a copy, as long thought — of Magna Carta, the medieval document that helped establish some of the world’s most cherished liberties.

It is one of just seven such documents from that date still in existence.

“I never in all my life expected to discover a Magna Carta,” said David Carpenter, a professor of medieval history at King’s College London, describing the moment in December 2023 when he made the startling find.

The manuscript’s value is hard to estimate, although it is fair to say that its price tag of under $30 (about $500 today) must make it one of the bargains of the last century. A 710-year-old version of Magna Carta was sold in 2007 for $21.3 million.

To help authenticate the document, researchers photographed it under ultraviolet light and then subjected it to various levels of spectral imaging, a technique which can enhance aspects of historical documents undetectable to the human eye.Credit…M.B. Toth/R.B. Toth Associates

Nicholas Vincent, a professor of medieval historyat the University of East Anglia, in eastern England, helped authenticate the text. He noted that the document, which bound the nation’s rulers to acting within the law, had resurfaced at a time when Harvard has come under extraordinary pressure from the Trump administration.