Basics: Latin Paleography
Section 5: Writing Supports and The Form of the Book: Papyrus and the Roll
A writing support is the surface on which the scribe writes.
Papyrus: In the ancient Mediterranean world, and in the wider Roman empire, the normal writing support was papyrus, which is made from the papyrus plant, a wetland plant with long, fibrous stems. (Think of the fibers in celery.)
To make papyrus into sheets one can write on, the pith of the long papyrus stem is soaked to soften it and sliced into long strips. A group of strips is laid side by side on a flat surface, then a second set of strips is laid on top of them, perpendicular to the first. The two layers are mashed together, which yields a strong sheet that is less likely to warp or tear than a single layer would.
You can see the fibrous texture of the resulting writing surface in this papyrus document from 2nd-century CE Syria:© The British Library Board, Papyrus 229.
Roll or volumen: Individual pieces of papyrus could be used for short documents, but for longer texts, numerous papyrus sheets would be joined into a long, horizontal writing surface that could be rolled from the ends. (Think of the side-to-side rolling of a Torah scroll, not the top-to-bottom rolling of the scrolls used by medieval heralds in movies.)
The papyrus would be rolled so that the side with the fibers running horizontally was on the inside. This was the surface that would be written on, and the scribe could use the fibers to guide the writing.
A papyrus roll is called a volumen in Latin (plural: volumina). This is where we get our word volume. A whole book would fill up many volumina — many volumes.