A single, monumental mappa mundi (world map), made around 1300 for Hereford Cathedral, survives intact from the Middle Ages. As Marcia Kupfer reveals in her arresting new study, this celebrated testament to medieval learning has long been profoundly misunderstood. Features of the colored and gilded map that baffle modern expectations are typically dismissed as the product of careless execution. Kupfer argues that they should rightly be seen as part of the map's encoded commentary on the nature of vision itself. Optical conceits and perspectival games formed part of the map's language...