From A Place for Everything, by Judith Flanders (Basic Books, 2020), Kindle pp. 127-129:
It is easy to assume that standardization, organization, regularization—and alphabetization—followed hard on the heels of the arrival of printing, but the reality was less tidy, as reality usually is. It took some time even to arrive at what we think of as a standard page of text: black ink on white paper, a centered text in roman type, intermittently interspersed with italic or bold, broken up into paragraphs by indented spaces, surmounted by running heads and page numbers. Nor were other elements of the book—chapter headings to mark text divisions, tables of contents, title pages to announce the book title, the author, publisher, and date and place of publication—any more formalized at this date. Instead, in the fifteenth and well into the sixteenth centuries, texts were designed to resemble manuscripts, often with no title page, and with red initial letters, headings, and glosses underlined. Paragraphs or other breaks in the text were rarely used, and most frequently unknown, although paragraph marks—¶—were sometimes used as marginalia, to give an indication of the text’s structure. Indented paragraphs would not become commonplace for another half century.
The Venetian printer Aldus Manutius (1449/52–1515) was an innovator: in his Hypnerotomachia Poliphili, The Dream of Poliphilus, printed in 1499, he used the paragraph indents we would recognize; and two years later, he introduced italic typefaces. Other symbols that we take for granted appeared more gradually. In manuscripts, a diple (which resembles our mathematical symbol meaning “less than”: <) had often hitherto been used as a marginal notation to guide readers’ attention to something important in the text. In the sixteenth century, the symbol moved into the text itself, indicating those lines of text that included sententiae, or citations from the authorities. And then, around the 1570s, the diple migrated again, to the beginning of a citation, to indicate direct speech or quoted material: it had become an inverted comma, or quotation mark.
Pagination—numbering each page with consecutive Arabic numerals—came relatively swiftly, although it was not originally a matter of marking first page 1, then its reverse page, and so on to the end of the work. At first, printers used these numerals to guide themselves, not their readers. From the early days of printing (and still today), the technology of the printing press was such that eight, sixteen, or thirty-two pages were printed together on a single sheet, which was then folded to produce pages 1 to 8, 1 to 16, or 1 to 32 of a book. That folded section was, and is, called a signature (the equivalent for a manuscript was a quire, which was usually made up of between four and six folded sheets), and multiple signatures were gathered in order and bound together to produce a book. These gathers can best be seen today along the top or bottom edges of most hardback books, where the pages meet the spine. To ensure the signatures were kept in the correct order during the binding process, printers gave each signature a number, or, today, consecutive letters of the alphabet, printing them inconspicuously at the bottom of each signature’s first page. The signatures could then be dispatched to a bindery in any order, and by following the progression of the numbers or letters, the book, even without numbered pages, would still easily be bound in the correct order.
Printed books were originally bound in plain paper covers, with the expectation that their owners would have them rebound in different styles or qualities of leather according to their resources and tastes. To ensure that the order of the signatures was maintained during this second binding, printers included a “register,” or list, of the first words of each signature, placing it at the beginning of the text in the position that a table of contents later came to occupy. And not long after the establishment of printing houses, some began to do more than give each signature a numeral for internal use. In printers’ technical vocabulary, a folio is the sheet of paper consisting of two sides, or pages, the front and reverse. Once the sheets have been bound into a book, the right-hand, uneven-numbered page is called the recto, the left-hand, even-numbered page the verso. (This page, for example, is a verso.) At first, it was the folios themselves that were numbered, followed by an “r” for recto, or “v” for verso. Whichever style was chosen, the numbers were no longer internal printers’ indicators, but were there for the convenience of the readers.
In 1450, fewer than a tenth of manuscripts used any system to indicate pagination. In 1499, a reference work to the epigrams of the Roman poet Martial, Cornu Copiae, The Horn of Plenty, by the Italian humanist Niccolò Perotti, may have been the first book to include numbering on every page, a novelty highlighted by the accompanying explanation at the head of the index: “[E]ach word that is sought can be found easily, since each half page [that is, each recto and verso] throughout the entire book is numbered with arithmetical numbers [meaning Arabic, not roman, numerals].” A century later, most printed books included page numbers as a matter of course.