The codex evolved from wooden tablets eventually replacing the scroll. The codex was random access, meaning that one was able to flip to any page. This is in contrast to scrolls which had sequential access. This meant that one would have to unroll all parts of the scroll that came before the part that one wanted to access. Random access was much more efficient.
The codex only contained words. Later, illuminated manuscripts were developed. These finely crafted books were adorned with illustrations and intricate detail. The monks who created these manuscripts were very skilled artisans who practiced craftsmanship, putting much work into an art form. This is important because by practicing their art, they were able to create beautiful manuscripts.
The format of the codex is still used today because of its random access principle which made it easy to look up information. It was also compact, durable, and portable. Modern objects that employ the codex format are encyclopedias, bibles, and