A codex Latin caudex for “trunk of a tree” or block of wood, book; plural codices is a book in the format used for modern books, with separate pages normally bound together and given a cover.Developed by the Romans from wooden writing tablets, its gradual replacement of the scroll, the dominant form of book in the ancient world, has been termed the most important advance in the history of the book prior to the invention of printing.[1] The spread of the codex is often associated with the rise of Christianity, which adopted the format for the Bible early on.[2] First described by the 1st century AD Roman poet Martial, who already praised its convenient use, the codex achieved numerical parity with the scroll around 300 AD, and had completely replaced it throughout the now Christianised Greco-Roman world by the 6th century.[3]

via Codex – Wikipedia, the free encyclopedia.