Term for the book form developed in the first post-Christian centuries, which replaced the previously typical scroll (see Rotulus). In the codex, rectangular sheets of parchment or paper are folded, combined into layers and bound together between two wooden book covers. Advantages over the scroll were the easier handling without unrolling and the ability to write on both sides of the sheets. Today, a codex generally refers to handwritten books that are mostly made of parchment.