A page from the Archimedes Palimpsest, one of the most important manuscripts surviving from antiquity, has been rediscovered at the Muse des Beaux-Arts in Blois, central France. The page was one of three lost decades ago, and only known from photographs taken in 1906.The Archimedes Palimpsest is a compendium of treatises by 3rd century B.C. Greek mathematician and inventor Archimedes of Syracuse. Archimedes was famous for inventions like his war machines and the screw pump that bears his name during his lifetime and throughout Late Antiquity, but his mathematical treatises were more obscure. The first compilation of them was copied by Isidore of Miletus, architect of Hagia Sophia, in Constantinople in 530 A.D. A copy of this compilation was created in Constantinople in 950 A.D. when Byzantine culture saw a renaissance of mathematical interest inspired by the former bishop of Thessaloniki, Leo the Geometer.The 10th century copy was dispatched to a monastery in Palestine after the Sack of Constantinople in April 1204 to keep it from being destroyed by the anti-Greek zealotry of the Crusaders looting the city. Unfortunately the remote monastery was not a safe haven either. In 1229 a monk sponged the ink off the parchment with lemon juice, cut the animal hide pages in half, turned them 90 degrees and filled them with prayers and liturgical texts.This practice of washing off and reusing parchment and vellum of older manuscripts was common in the Middle Ages because new pages made from animal skin were very expensive to produce. They were also durable enough to withstand this harsh form recycling, and even the ink turned out to be able to withstand the attempt to obliterate it. The cleaned parchment pages still contained traces of the ink under the surface, and over time, the shadow of the original writing would reappear. Texts with ghosts of previous texts are known as palimpsests.The Archimedes Palimpsest stayed in the hands of the Greek Orthodox church for another 700 years. It was catalogued in Istanbul in the early 20th century, and was thoroughly documented and photographed by Danish historian Johan Heiberg in 1906. A great deal of the original Archimedean text was faint but visible, and could be read with a magnifying glass. Heiberg published a translation of the original texts hed been able to decipher in 1915.The manuscript went missing in 1922 when the Ottoman Sultanate was abolished and the Greek Orthodox library in Istanbul had to be evacuated. The year after that, it was in the hands of a Parisian businessman Marie Louis Sirieix who obtained it under very sketchy circumstances. He claimed to have bought it from a monk, but there was no proof of that. He or someone he allowed access to the manuscript added four illustrations of the Evangelists in faux Byzantine style, evidently trying to make it look like a medieval illumination.Sirieix never did resell it, and it was stashed in his cellar until the 70s, subject to water and mold and missing three pages lost somewhere in in its vicissitudes after 1906. His daughter finally put it up for auction at Christies in 1998. It was bought by an anonymous collector (rumor has it the winning bidder was Jeff Bezos) who then lent it to the Walters Art Museum in Baltimore for conservation and analysis. A few years later, the manuscript, minus the three lost pages, was scanned with multispectral imaging technology revealing new original texts.The leaf identified in Blois by Victor Gysembergh, a CNRS researcher at the Centre Lon Robin for Research on Ancient Thought (CNRS/Sorbonne University), was among these missing pages: comparison with Heibergs photographs, now preserved at the Royal Danish Library, made it possible to confirm without ambiguity that it was leaf number 123.On one of its two sides, a text of prayers partially covers geometric diagrams and a passage from the treatise On the Sphere and the Cylinder, Book I, Propositions 39 to 41, much of which remains largely legible. The other side is covered by an illumination added in the twentieth century, depicting the Prophet Daniel surrounded by two lions, beneath which the ancient text remains to this day inaccessible using conventional methods of examination.Now that the missing leaf has been identified, researchers hope to get permission to use the latest synchrotron-based X-ray fluorescence analysis to fully expose the original writing impressions.