(Much of this information is undated, because we don’t have any exapmples of these bindings left. It’s based on pictures, later books, and a certain amount of guesswork.)
In the beginning was papyrus, made from the fibrous stems of a swamp plant that grows by the Nile. It was cheap, easy to make, took ink well, and lasted forever, but it didn’t fold. So the Egyptians, Greeks and Romans all made scrolls.
These scrolls weren’t formatted the way you’re think they were. The text wasn’t written line by line down the scroll – portrait format, if you will. Instead, it was written in blocks, side to side, so a reader could read with a roll of papyrus in each hand, unrolling with one hand and rolling with the other to move through the text.
Over time, civilisation moved out of the swamplands beside the Nile, and papyrus became less convenient. Scribes cast about for new materials, and ended up with parchment, or vellum. This is the inner hide of either a sheep or a cow. It’s whiter than papyrus, more durable, and you can get sheep and cows everywhere. (It’s more pricey, but until Gutenberg, the most expensive part of the book was the writing inside it. Material costs were immaterial.)
One day someone got hacked off at scrolls. Maybe one too many got squashed – that leaves hundreds of narrow strips of papyrus to try to stick back together. Not fun. Or perhaps yet another pile of cylindrical scroll casings fell down on someone’s foot after the library equivalent of an avalanche.
So they started fan-folding the vellum scrolls (this is why it matters that they were written landscape style.) It was a logical extension of the idea to sew one set of folds together, so that the book held together nicely.
Not much later, some bright spark realised you could get more book out of every sheep by writing on both sides of the parchment* rather than fan-folding it. And you didn’t have to paste the sheepskins together to make a long roll. All you had to do was take a bunch of rectangles, fold them up, sew them together at the folds, and hey, presto! It was like the Mac revolution.
Thus was the codex born: the sewn book block that we now know and love.
* The Japanese, who used rice paper, made a different transition. Their inks penetrated the papers too much to print on both sides, so they folded the papers in half with the raw edges at the spines. This leads to some clever things you can do in spy novels, writing inside the folded sheets. But I digress.
Originally posted on Making Light