The history of the written word, tautologically, extends back to the beginning of non-oral history itself. It predates books, certainly. But it also predates paper. Paper was first developed by the Chinese nearly 2000 years ago but was not manufactured by Europeans until the 14th century. Indeed, not until 1588 would England have its first commercially successful paper mill. So what did European print books on before paper was widespread? Parchment — a material made from the hides of animals, and commonly that of sheep.

One of the world’s most revolutionary inventions, the printing press, was developed by Johannes Gutenberg in the early-to-mid 1400s. Gutenberg’s printing press, first operational in 1450, used both paper and a parchment called vellum to produce, famously, the Gutenberg Bible. The print run was a work in progress even when in progress itself. At first, Gutenberg put 40 lines on a page, so the first-run pages of each copy share this trait. All other pages (except one, which has 41 lines) have 42 lines per page. While the reasons behind this are hard to know for certain, the most likely theory is that Gutenberg was trying to conserve paper — it was, after all, still a hard-to-obtain item.

But one thing was not up for debate: the size of the pages themselves. There, Gutenberg deferred to the practice of bookmakers and pamphleteers prior. And by and large, we’ve maintained those sizes since. The standard? According to Got Medieval, it’s the size of a sheep’s hide, with the rounded edges trimmed to create a rectangular shape, as pictured above. The rectangle, folded over twice, yields eight printable pages (four pages, front and back), and is roughly the size of modern-day reference book such as an encyclopedia. Fold it again and you end up with 16 pages and a smaller book size — one which matches up well to the standard hardcover novel. In a very real sense, the books we read are proportional in size to medieval sheep. (And given that digital technology follows print, the same is true to the screen size of an Amazon Kindle.)

Bonus fact : It’s “common knowledge” that you can only fold a piece of paper eight times before an additional fold becomes impossible. It turns out that the common knowledge is incorrect — paper can be folded as many as 12 times, depending on the length and thickness of the sheet in question. That’s a good thing, too, because if you folded a piece of paper in half 42 times, you’d reach the moon.

From the Archives: Paper Trail: Your photocopies may have tiny yellow dots — intentionally, but mostly hidden.

Related: “Living With Sheep: Everything You Need to Know about Raising Your Own Flock” by Geoff Hansen. 28 reviews, averaging 5 stars.