In the ancient world, written material could be found in many forms on many materials. (See Ancient Writing Materials for examples). For long works, such as literary texts, the most popular form by far was the papyrus roll. Rolls were also used for documentary texts, such as government records of taxpayers. Towards the end of the Roman era, however, use of the roll began to decline as the codex became more popular.
A classical papyrus roll (or "bookroll") differs slightly than the scroll that most modern people imagine. Contrary to people's misconceptions, a bookroll is read "sideways". Many people imagine scrolls that unroll vertically, probably based on what they've seen at the movies. This use of the roll, illustrated below on the left, is characteristic of the Byzantine era (4th - 7th centuries A.D.). In the classical era, the roll would be written in a series of columns read horizontally, as illustrated below on the right.
Classical-era papyrus roll
The classical-era roll is actually quite handy, although to a modern reader it might seem a bit clumsy at first. The roll can easily be read column by column from left to right. This concept is illustrated below (click on the roll to watch it in action). In actual practice, a person reading a scroll would only need to expose a single column at a time, keeping the remainder of the text neatly rolled up on either side.
Papyrus rolls like this were kept in the great library of Alexandria and stored in cubbyholes or on shelves. Some rolls might feature wooden pegs attached at the two ends for easier handling, or a tag containing the author's name and the title of the text, but these were optional features.
The papyrus roll remained the standard form of the ancient book until around the 4th century A.D., when the codex (similar to a modern book) gradually became more popular. Just like modern books, ancient codices often included page numbers at the top of each page (this practice also appears in some rolls, where each column, rather than each page, was numbered). Codices came to be associated with Christianity, as early Christian works were often written in codices rather than rolls (although examples of both forms can be found), and ultimately the roll died out in all uses, Christian and non-Christian.
A codex could consist of a single quire or several quires bound together. A quire is simply a grouping of leaves. Leaf is the term used for a page of a codex (technically, each leaf has two pages: for example, pages 1 and 2 might appear on opposite sides of the same leaf). See an example of a four-leaf quire and how it was made.
Parchment vs. Papyrus
Around the same time that the codex replaced the roll, papyrus came to be replaced by parchment (animal hide) as the favored writing material. Although the overall effect was a transition from the papyrus roll to the parchment codex, the materials are not necessarily linked to the different formats. Papyrus codices are not uncommon, and parchment rolls have been found. Parchment may have become more popular as the necessary technology to create fine leather spread, and parchment had the added advantage that it could be made anywhere, while papyrus could only be grown in the Nile region.