“Books” were, once upon a time, created as scrolls rather than sets of bound pages (technically called “codexes”). Scrolls have a lot going for them; they can be of any length, and they don’t present any of the issues created by having to shift from one page to the next when you’re reading, or for that matter when you’re writing.
But one really important advantage codexes offered over scrolls is that it’s a lot easier to use both sides of each page in a codex than it is to write (or read) on the back of a scroll. There are, of course, some ancient scrolls that are inscribed on both sides. Those are called “opisthographs.” The word comes from the the Greek “opistho” (behind” and “graphos” (written). Most codexes are “opisthographic,” while most scrolls are “anopisthographic,” or written on just one side.
Scrolls had some other interesting advantages, at least if you enjoy impossibly obscure words. For example, you can’t store scrolls quite the same way you store codexes (on a shelf) because the scrolls tend to roll around. So instead you’d have a sort of cupboard for them, where you could pile some up and the sides of the cupboard would keep them from rolling away. That cupboard is called a “scrinium.”
Not only that, but have you ever heard the phrase “the whole magilla?” That originally comes from the word “megillah”, which means “the whole thing.” That meaning is based on its earlier meaning, which was “a long and complicated story.” And that meaning had to do with a scroll — specifically the Hebrew “megillah”, which meant a scroll — specifically the five books of the Hebrew scriptures. Which, like the Torah (which is longer), is a scroll.