How was a lost book by Archimedes found hidden under a prayer book?

A book by Archimedes survived because a medieval scribe recycled it. In 1229, near Jerusalem, a copy of his works made around AD 950 was taken apart, scraped, washed and reused to write a prayer book. Parchment was precious, and the region was in turmoil. The prayers went on top, but faint traces of the Greek mathematics stayed underneath. A page reused like this is called a palimpsest.

Nobody noticed what it was for centuries. In 1899 a catalogue of a church library in Constantinople copied out a few lines of the hidden text, and the great Archimedes expert Johan Heiberg recognized them at once. In 1906 he photographed the pages and confirmed that they contained works thought to be lost, including the only known copy of The Method of Mechanical Theorems, where Archimedes explains how he discovered his results.

Then the book vanished. It disappeared in 1922, spent decades hidden in a businessman's cellar, grew mould, and a forger even painted fake gold portraits over four pages to raise its price. It resurfaced at a New York auction in 1998, sold for $2 million to an anonymous buyer, who lent it to the Walters Art Museum in Baltimore. There, ultraviolet, infrared and X-ray imaging finally read what the scraping, mould and gold had hidden.