Print media evolved into its present forms.
In, say, 1469, there were no page numbers. This obvious and now necessary part of the book’s user interface simply did not exist.
The earliest extant example of sequential numbering in a book (this time of ‘leaves’ rather than pages, per se) is the document you see at the top of this page, Sermo in festo praesentationis beatissimae Mariae virginis, which was printed in Cologne in 1470. The practice didn’t become standard, the wonderful I Love Typography tells us, for another half century.
The page number is particularly interesting, I think, because it is a pointer, a kind of metadata that breaks apart a work into constituent parts. The existence of page numbers creates a set of miniature sub-publications to which someone can refer.
Read more. [Image: Heinrich Heine Universität Düsseldorf]