Technically speaking, the definition quoted above is for the Codex variety of book.
https://en.m.wikipedia.org/wiki/Codex
Before AD300 the variety of book in most common use was the scroll. Since it took the codex 600 years from introduction to domination there must've been some serious resistance to the more expensive format despite its increased convenience. I'm guessing it took the invention of the bookmark to convince the last holdouts. Or a military expedition.
