Pocket Book: Aldus Manutius 2
Aldus Manutius, the great early Venetian printer and publisher.
Aldus introduced "smaller editions of the classics that would be more affordable and portable than the folios and quartos that were then common. He commissioned Francesco Griffo to cut a type based on the humanistic cursive script, which today we call Italic."
So italics began not as emphasis as we use it today, but instead as a narrower, more compact body text face. Aldus published smaller book formats, on lighter and less expensive vellum, that fit into a pocket. This was the original "mass market paperback!"
From the exhibition Early Italian Books at the John Hay Library at Brown University.
See also Wikipedia entry on Aldus Manutius