Parchment was expensive in the medieval world, and a monk needing pages for a new prayer book did not always start with a blank sheet. In thirteenth century Byzantium, a scribe assembling a Euchologion, a book of prayers for the church's liturgy, took older manuscripts apart for their parchment, scraped the existing ink away as thoroughly as the technology of the day allowed, cut the larger sheets down, rotated them ninety degrees, and folded them to the new book's smaller size. One of the manuscripts fed into this recycling was a tenth century copy of seven mathematical treatises by Archimedes, the ancient Greek mathematician whose work on geometry, mechanics and what would later be called calculus had already been rare and precious even before a monk scraped it away to make room for prayers.
The erasure was thorough enough to fool centuries of readers, but not perfect. Faint ghost traces of the underlying Greek mathematics remained visible under the right conditions, and in 1906 the Danish philologist Johan Ludvig Heiberg spent days in Constantinople reading what he could of them with a magnifying glass, recognizing text from two treatises, the Method and the Stomachion, that survived nowhere else in the ancient record. The manuscript then vanished from scholarly view for most of the twentieth century, its exact whereabouts unknown, before resurfacing decades later in circumstances nobody studying it in 1906 could have predicted.