A librarian at the University of Reading has rediscovered some of the first pages ever printed in England, according to the BBC.

The two-sided page, found hidden in the library’s archives, is from one of the first books printed by William Caxton, who set up the first printing press in England and became the country's first book retailer. Printed sometime in late 1476 or early 1477, the pages were part of a handbook for medieval priests called Sarum Ordinal.

The leaf is not just rare, but one of a kind. No full copies of the book have survived, though the British Library holds eight other double-sided leaves out of the original 160. These recently located pages are from a different part of a book than those at the British Library.

Librarian Erika Delbecque holds up the Caxton leaf.Courtesy the University of Reading

At one point, the leaf of paper had been pasted into another book to reinforce its spine, according to special collections librarian Erika Delbecque, who found it while cataloging materials in the library. In the 1820s, the leaf was discovered by a Cambridge librarian and taken out of that book, but that librarian didn’t know that it was a Caxton-printed page. Delbecque found it in the collection of John Lewis, a typographer whose papers the University of Reading purchased in 1997.

“I suspected it was special as soon as I saw it,” she says in a press release. “The trademark blackletter typeface, layout, and red paragraph marks indicate it is very early western European printing. It is incredibly rare to find an unknown Caxton leaf, and astonishing that it has been under our noses for so long.” The early printing specialist who evaluated its authenticity estimates its worth at up to $129,000.

The pages will be on display to the public at the MERL Museum in Reading until May 30.

[h/t BBC]