Between about 150 and 450 CE the form of the manuscript book shifted from the roll to the codex. However, the transition was very gradual as the traditional roll format had been functional for over 2000 years. The transition may not have been "complete" until the fifth century.
"Ultimately, as its etymology indicates, the codex book evolved from wooden tablets, often with wax-filled compartments, used in ancient Rome for more or less ephemeral jottings and figurings. A group of such tablets, tied or hinged together, was known as a caudex / codex, a word originally indicating a tree trunk or block of wood (and, in Terence, a blockhead). At some stage before the Christian era folded parchments (membranae) came to be used for the same ephemeral purposes, and then were eventually adopted for permanent storage of written matter, even literary texts; and by the third century A.D. the term 'codex' had become assimilated also to these non-wooden objects" (Needham, Twelve Centuries of Bookbindings 400-1600  4).
The fourth century saw a revolution in book production which made it possible to make books large enough to hold the whole Bible in one volume. Of these, the Codex Sinaiticus and the Codex Vaticanus survived to the present. The codex also allowed the development of bindings which were protective as well as decorative. Bindings would have increased the longevity of codices versus rolls, and over time this would have been recognized as a significant advantage. T.C. Skeat also argued that there may have been cost savings in the production of information in codex form versus the traditional papyrus roll.
In his brief but highly significant monograph, Early Christian Books in Egypt (2009) Roger Bagnall took issue with the traditional view that closely associated the development of the codex with early Christianity, showing that the number of surviving Christian documents in codex form relative to the number of surviving non-Christian documents in codex form during the transitional period from the first through fourth centuries CE is proportionate to the overall percentages of Christian versus non-Christian documents surviving from the period. These statistics he correlated with the ratio of estimated Christian population versus the non-Christian population in Egypt during the same period. He also documented the high cost of producing books by hand during the first centuries of Christianity, showing that book ownership would mainly have been limited to government, the moneyed classes, or religious institutions, thus bringing into doubt the notion that Christians adopted the codex form of the book because it was associated with a form of notebook used by the "common man." One of the numerous examples he used is the so-called Theban Magical Library, a collection of non-Christian books, including many of the most famous magical papyri, which was acquired by institutions in Leiden and London in the nineteenth century, possibly from a single find in a tomb in the West Bank at Thebes, Egypt. Five of the thirteen items in this library are fourth century codices; eight are third century rolls. Bagnall observes that the dates of the rolls versus the codices correspond to the time in which the codex form is thought to have become dominant, the fourth century. His other observation was that these collections of Egyptian magical spells can in no way be called Christian documents. He concluded by retracing the origins of the codex to the Roman use of tablets strung together, suggested that no neat explanation for the transition from the roll to the codex will be found, and suggested that this transition in the form and function of the book was a "social and cultural transformation" that occurred over several centuries throughout the Roman empire, resulting from the "choice by local elites to adopt Roman ways."