David Rubenstein and his $23.1 million, 800-year-old piece of parchment.

Private equity billionaire David Rubenstein has become something of a patron saint for D.C.’s treasured cultural possessions recently, donating $4.5 million to save the National Zoo’s panda program and another $7.5 million to repair the Washington Monument. But his biggest philanthropic passion is buying pieces of paper—-really, really old ones.

He owns the Emancipation Proclamation, which hangs in the Oval Office. He’s got the first map of America, on loan to the Library of Congress. Other various and sundry documents rest in the National Archives, and this morning, Rubenstein unveiled the best prize yet: An original copy of the Magna Carta, nearly 800 years old, which had been painstakingly restored by the Archives’ staff and placed in a $322,000 aluminum encasement filled with inert gas.

The Carlyle Group co-founder came by his document-collecting habit honestly, as chief counsel to the Senate subcommittee that deals with constitutional amendments in the 1970s. And he’s a little obsessive about it. At the big reveal, a reporter asked the officials present if someone might briefly summarize the Magna Carta’s history.

“Yes,” Rubenstein answered quickly.

An Archives staffperson hesitated. “Actually, we…”

“I can do it,” Rubenstein cut her off, before launching into a two-minute soliloquy on how the thing got written. “In 1215, in Runnymede, the noblemen came together with King John, and they insisted on certain principles, so they would not feel that they wouldn’t be taxed without representation…”

Rubenstein eventually came to the end of the story, but he’s happy to chatter on about it as much as you want. Thora Colot, executive director of the Foundation for the National Archives, describes his behavior in the Archives’ rotunda: “He’s giddy,” she said. “He’s like a little kid.”

What could Rubenstein save next? It’s unpredictable. He says he’s got a couple more historical documents in mind, but if something else in the District falls apart, a lot of glances will be cast hopefully his way.

Listen to Rubenstein’s lecture here:

[audio:http://www.washingtoncitypaper.com/blogs/housingcomplex/files/2012/02/Rubenstein-on-Magna-Carta3.mp3|titles=Rubenstein-on-Magna-Carta]

Photo by Lydia DePillis’ iPhone