“The pages of most books were of mottled parchment, that is, dried sheepskin, which was . . . nowhere more abundant than in Ireland, whose bright green fields still host each April an explosion of new white lambs. Vellum, or calfskin, which was more uniformly white when dried, was used . . . sparingly for the most honored texts. . . . It is interesting to consider that the shape of the modern book, taller than wide, was determined by the dimensions of a sheepskin, which could most economically be cut into double pages that yield our modern book shape when folded.”

—Thomas Cahill, How the Irish Saved Civilization: The Untold Story of Ireland’s Heroic Role from the Fall of Rome to the Rise of Medieval Europe, 1995.