Several of Archimedes’s treatises were found on a palimpsest, a manuscript that has been scraped and washed so that another text can be written over it, thus reusing the expensive parchment. Reusing parchment was a common practice in the Middle Ages, but the original text can sometimes be reconstructed. Using digital processing with several types of light and X-rays to study this thirteenth-century-C.E. prayer book, scientists were slowly able to decipher the texts by Archimedes that were underneath, including one that had been completely lost. (Image by the Rochester Institute of Technology. Copyright resides with the owner of the Archimedes Palimpsest, but digital images of the entire manuscript can be found at www.archimedespalimpsest.org.)