The palimpsest is believed to have been created by Byzantine monks in the 13th century, probably in Constantinople. As was the practice then, the durable and valuable vellum pages of several older texts were washed and scraped, to remove their writing, and then used for a medieval prayer book. The pages of the older books became the sheaths of a newer one, thus a palimpsest (which is pronounced PAL-imp-sest and is Greek for “rubbed again”).

Image Professor Judson Herrman examines the Archimedes Palimpsest. Credit... Ken Cedeno for The New York Times

After the Christie’s sale the manuscript was left at the museum by the private collector for conservation and study. This year imagers at Stanford University used powerful X-ray fluorescence imaging to read its final pages, which are being interpreted, transcribed and translated by a group of scholars in the United States and Europe.

The new Hyperides revelations include two previously unknown speeches, effectively increasing this renowned orator’s body of work by 20 percent, said Judson Herrman, a 36-year-old professor of classics at Allegheny College in Meadville, Pa. He is one of a handful of classicists who have written doctoral dissertations on Hyperides.

Hyperides lived from 390 or 389 B.C. until 322 B.C. and was an orator who made speeches at public meetings of the citizen assembly. A contemporary of Aristotle and Demosthenes, he wrote speeches for himself and for others and spoke at important political trials. In 322 B.C. Hyperides was executed by the Macedonians for participating in a failed rebellion.

“It’s a spotlight shining on an important moment in history,” said Mr. Herrman, currently a fellow at the National Humanities Center in Research Triangle Park, N.C. Until the new leaves were found in the palimpsest, most scholars believed only fragments of Hyperides survived beyond the Classical period. The mystery of Archimedes’ treatise on combinatorics, the Stomachion, was solved in 2003 by deciphering the palimpsest. Now W. Robert Connor, the president of the Teagle Foundation, which provides education and financial resources for education, called the discovery of new Hyperides text a “tour de force of the first order.”