The last remaining copy in the United States and the last in private hands of the Magna Carta, one of 17 known to exist, was sold on Tuesday by the Perot Foundation, created by Ross Perot, the billionaire former US presidential candidate, to make philanthropic grants.
The foundation had acquired it from the collections of the Brudenell family of Deene Park in Northamptonshire in 1984.
"It's a good day for our country," said David Rubenstein, a lawyer and founder of the Carlyle Group, a private equities firm after he made the extraordinary purchase.
He said he had arrived just minutes before the sale and very nearly missed out.
"I was determined to do what I could to see that the National Archives can continue to display this," Rubenstein said, noting that the 1297 document was the basis for both the US Constitution and the Declaration of Independence.
"I am really just a temporary custodian of it," he said, adding that he would not have to travel far to see the document as his office is just a few hundred yards from the National Archives.
'Most important document'
The Magna Carta, which Sotheby's called "the most important document in the world," established the rights of the English people and curbed the power of the king.
"I don't think you can put a price on freedom"
the buyer, on how high he was willing to bid for the copy
The US Constitution includes ideas and phrases taken almost directly from the charter, which rebellious barons forced their oppressive King John to sign in 1215.
The Magna Carta was ratified and reissued with each monarch who succeeded John. It was enacted as law in 1297 by the British parliament when it was reissued by King Edward I. The copy sold on Tuesday is from 1297.
Asked how high he was willing to bid for the Magna Carta, Rubenstein replied: "I don't think you can put a price on freedom."
When it announced the auction in September, Sotheby's said the document was valued at up to $30 million. The final $21,321,000 price included Sotheby's commission.
The record for a document or manuscript at auction is held by Leonardo da Vinci's "Codex" manuscript, which sold for $30.8 million at Christie's in 1994.