Codex

A codex (Latin caudex for "trunk of a tree" or block of wood, book; plural codices) is a book made up of a number of sheets of paper, vellum, or similar, with hand-written content, usually stacked and bound by fixing one edge and with covers thicker than the sheets, but sometimes continuous and folded concertina-style. The alternative to paged codex format for a long document is the continuous scroll. Examples of folded codices are the Maya codices. Sometimes the term is used for a book-style format, including modern printed books but excluding folded books.

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. The spread of the codex is often associated with the rise of Christianity, which adopted the format for the Bible early on. First described by the 1st-century AD Roman poet Martial, who praised its convenient use, the codex achieved numerical parity with the scroll around AD 300, and had completely replaced it throughout the now Christianised Greco-Roman world by the 6th century.

The codex holds considerable practical advantages over other book formats, such as compactness, sturdiness, ease of reference (a codex is random access, as opposed to a scroll, which is sequential access), and especially economy of materials; unlike the scroll, both recto and verso could be used for writing. Although the change from rolls to codices roughly coincides with the transition from papyrus to parchment as favourite writing material, the two developments are quite unconnected. In fact, any combination of codices and scrolls on the one hand with papyrus and parchment on the other is technically feasible and well attested from the historical record.

Although technically even modern paperbacks are codices, the term is now used only for manuscript (hand-written) books which were produced from Late antiquity until the Middle Ages. The scholarly study of these manuscripts from the point of view of the bookbinding craft is called codicology; the study of ancient documents in general is called paleography.