The Ymago mundi is a compendium of late medieval cosmographic speculation, composed by the French theologian Pierre d’Ailly (1351-1420) with references to Ptolemy and drawing largely on Roger Bacon’s groundbreaking work on natural science, Opus maius (1267). It was this very edition that Christopher Columbus read and employed in preparation of his enterprise (Columbus’s copy, with his handwritten marginalia, is now preserved in Seville). The JCB’s copy was also studied and annotated – by at least one contemporaneous reader and several later ones – proving the importance of d’Ailly's cosmographic theories well into the early modern period. The opening pages present rich annotations of cosmographic diagrams and detailed maps of zones and climates. Some passages refer explicitly to the feasibility of a transoceanic navigation from Spain to the Indies, providing a template for what Columbus and other early pilots would have used to cross the Atlantic. This book is one of the earliest of the JCB’s collection of early cosmographical texts and maritime guides that provide an introduction to the cosmographical imagination of the late Middle Ages as European exploration and colonization began in earnest around the globe.