codex

A codex is a book made of bound pages arranged along a spine, rather than a scroll rolled from end to end. The word derives from Latin codex, originally meaning a trunk or block of wood and later a book or document. In the ancient world, the codex form gradually replaced the scroll for many texts.

The transition to codices occurred in the first few centuries CE, gaining popularity in late antiquity and the early Middle Ages. Benefits included easier reference and navigation, the ability to include multiple texts in one volume, and better preservation. This format became standard for Christian scriptures, classical works, and legal codes.

Medieval codices were commonly written on parchment or vellum and often decorated with illumination, marginal notes, and concordances. Later, paper became common. Typical features include chapters or sections, tables of contents, and index systems. The codex contrasts with the scroll as a portable and more navigable form of book.

Notable examples include Codex Sinaiticus and Codex Vaticanus, both from the 4th century and among the oldest extant Christian Bibles in Greek; Codex Alexandrinus (5th century); and Codex Bezae Cantabrigiensis (5th century). In law, the Codex Justinianus is a definitive compilation of Roman law prepared under Justinian I.

In modern usage, codex may refer to any bound manuscript. The term also appears in digital contexts, such as OpenAI Codex, an AI system that translates natural language into code and underpins coding assistants.