Three leaves had been missing for more than a century. Researchers found one of them when they decided on a whim to check the archives of a French museum

Prayers partially cover diagrams from On the Sphere and the Cylinder , a treatise written by Archimedes. © Blois, Musée des Beaux-Arts / IRHT-CNRS

A leaf from a medieval manuscript containing ancient Greek mathematical treatises has been rediscovered in the archives of a French museum. Previously, historians assumed the rare page had been lost to history.

Known as the Archimedes Palimpsest , the manuscript is a 177-page document created in the tenth century C.E. It contains rare copies of treatises by Archimedes , the third-century B.C.E. mathematician, along with writings by other authors.

“This book never ceases to give up its secrets,” William Noel , a curator of ancient manuscripts at the Walters Art Museum, told Smithsonian magazine ’s Mary K. Miller in 2007.…