In 1998, Christie's Auction House of London auctioned off a musty old prayer book for two million dollars. 

What they thought was just a prayer book contained Greek inscriptions and accompanying diagrams that turned out to be the only surviving copies of several works by Archimedes from over 2,000 years earlier. And the researchers discovered that Archimedes was working out principles that, centuries later, would form the heart of calculus and that he had a more sophisticated understanding of the concept of infinity than anyone had realized.

Though Archimedes wrote his manuscript on a papyrus scroll 2,200 years ago, someone later copied the text from papyrus to animal-skin parchment. Then, 700 years ago, a monk needed parchment for a new prayer book. He pulled the copy of Archimedes' book off the shelf, cut the pages in half, rotated them 90 degrees, and scraped the surface to remove the ink, creating a palimpsest—fresh writing material made by clearing away older text. Then he wrote his prayers on the nearly-clean pages.