Codex is the word used to indicate that form of content holder which we think of as a book: a bunch of folded pages held together on one side and conventionally, but not necessarily, protected by some sort of cover. It can also be used to indicate a manuscript volume: The Codex Sinaiticus is a famous example. Indeed The Oxford English Dictionary gives this as its single bookish definition, ignoring the folded book/not-scroll definition, which meaning has presumably evolved in the last century or so, maybe as a result of the growth of book history as an academic subject: this OED entry is one of those not revised since 1891. They cite a listing of recipes for medicines as their only other non-obsolete meaning for codex. My school Latin dictionary (published by Cassell & Co. in 1927) gives “codex, codicis, m, = caudex, trunk of a tree; a book, composed of wooden tablets, covered with wax; a book, document.” This all seems a bit more definite than other sources suggest: but maybe there really are Latin documents which use codex in the sense of wax writing tablet. The editor, Professor Thomas, is obviously plumping at least for the derivation of the bound book from wax tablets. But if we are starting off with caudex, a tree trunk, log, block of wood, ending up with “book” may a bit of a stretch, but there are theories. Perhaps we’ll have to await the OED editors’ adjudication when they get around to updating this entry.

The development of the codex is often held to be associated with the Christians in 2nd century Rome. The earliest known reference however is from Martial in the 1st century who encouraged his readers to buy his poems in this new format. “You who long for my little books to be with you everywhere and want to have companions for a long journey, buy these ones which parchment confines within small pages: give your scroll-cases to the great authors – one hand can hold me.” Sounds a bit like paperbacks for railway journeys, doesn’t it? I still like my suggestion that the preponderance of early codex volumes from Christian sources is not a result of there being more of them in the first place. Rather I suspect it was a result of differential survival rates. Monks would no doubt go to considerable trouble to hide their codices — they well knew how laborious they were to create — and would clearly be more motivated to save the devotional literature on which their life was grounded rather than those bulky pagan classics, while reading laymen, thin on the ground anyway, might be less heedful about their books when the Vikings were landing. Thus more “Christian” codexes would survive the times of trouble, no matter whether there were more or fewer of them at the start. It’s dangerous to draw conclusions from the absence of evidence, but we shouldn’t altogether ignore it in making our guesses.

To come up with the idea of the codex we did first have to “invent” the page. Scrolls, the functional predecessors of the codex, weren’t of course written in mile-long lines; their text was indeed divided up into blocks which could be said to resemble pages. They were only written on on one side though. Some papyrus pages were first found at Oxhyrynchus in Egypt, written on both sides and thus presumptively from things we’d call books rather than scrolls. The presence of page numbers is also diagnostic — they were obviously not needed if you were just unrolling a scroll as you read. But papyrus was liable to break when folded, and was in any case more suited to the hot dry climate of Egypt than to Europe’s more humid environment. We can say with some confidence that the codex format couldn’t really take off till there was a regular supply of parchment. Exactly when parchment was invented, or more importantly was perfected is not know. Herodotus says that writing on skins was common in his time, the 5th century BC, but what’d be needed would be a regular supply of good quality, and we can only speculate rather circularly that such conditions began to appear in 1st century Rome, as attested to by Martial.

Keith Houston’s The Book has just been published, and is, as I’ve said in my review, an invaluable resource on many topics including this one. Here’s a piece of his for BBC.com about the origins of the codex.