 Most medieval manuscripts, illuminated or not, were written on parchment (most commonly of calf, sheep, or goat skin), but most manuscripts important enough to illuminate were written on the best quality of parchment, called vellum.Beginning in the Late Middle Ages, manuscripts began to be produced on paper.Very early printed books were sometimes produced with spaces left for rubrics and miniatures, or were given illuminated initials, or decorations in the margin, but the introduction of printing rapidly led to the decline of illumination.