A palimpsest is a page used twice; the word is Greek for “scraped again.” Parchment was dear, so in 1229 a scribe who seems to have been called Ioannes Myronas took an old copy of Archimedes, nearly three centuries old, scraped the writing off its leaves, turned them sideways, and wrote a prayer book across them. Among what he erased was the only known copy of the Method. Every other copy is lost, including, presumably, the ones nobody ever laid a blade on. A book of geometry that few could follow had little reason to be kept, and a prayer book had a reason every day of the year. All he wanted was the parchment, and he put Archimedes in the one kind of book someone would go on looking after.