Garry Wills, Augustine’s Confessions: A Biography, Lives of Great Religious Books (Princeton: Princeton University Press, 2011), 1–4:

How did Augustine write Confessions?

Well, in the strict sense, he didn’t—didn’t set words down on papyrus or parchment.

Augustine has been painted, by artists as great as Botticelli, Carpaccio, and Benozzo Gozzoli, seated at a desk and writing. He did not do that.

Oh, he undoubtedly wrote things like notes to himself, or lists of items, or instructions to individual brothers in his monastic community.

But the books, sermons, and letters that have come down to us were all dictated to scribes.

Even a book that feels as intimate as Confessions was spoken to several of the many scribes Augustine kept busy. That was the normal practice in antiquity. Even in prison, Saint Paul had a scribe on hand. Even when living as a hermit, Saint Jerome had teams of scribes. The population of ancient scribes was a vast one.

Writing was a complex and clumsy process. That was especially true in the classical period, when papyrus scrolls were used. One needed at least three hands to unroll the scroll on the left, to roll it up on the right, and to write a series of columns in the intermediate spaces.

Besides, even the mixing of the ink and trimming of the reed pens (quills arrived in the Middle Ages) had to be done while the scroll was held open at the spot reached by the scribe.

Since the rolls were written on one side only, they could run to great lengths, as much as thirty feet long.

Obviously, the author could not be doing all this and composing in his mind.

The only efficient way to function was for the author to dictate to a shorthand writer (tachygrapher), who took the text down on tablets of wax or wood.

Then this first scribe, with the help of assistants, would write the text on a scroll.

Other scribes would copy this text on other scrolls—the only way to duplicate a text in the age before printing presses.

A man would read slowly from the master text while a number of scribes created their own copies.

There was no need for these secondary scribes to decipher the first man’s shorthand signs. After he made the master copy, multiple facsimiles were needed. . . .

Writings, created with such labor, could be lost in transit where couriers were careless or in peril—Augustine’s first letter sent to Jerome did not reach him, causing endless later trouble. Books could easily disappear if there were not enough copies made or preserved.  Even though Augustine kept his own archives in good order, his very first book is irretrievably lost.

Teams of scribes had to be kept at work all the time to bring a book into existence and keep it there. The Late Antique church historian Eusebius tells us that the church father Origen had seven tachygraphers and a horde of other scribes and calligraphers to replicate what the shorthand experts took down and wrote out (History of the Church 6.23).

The making of books was an expensive as well as laborious and time-consuming process.

One of the principal costs of Augustine’s episcopal establishment was the production of his many books. He wrote five million words that have come down to us, most of them after he became the bishop of Hippo. Isidore of Seville famously said that anyone who claims to have read all of Augustine must be a liar. In a recently discovered letter (Divjak 23-A), Augustine says that in less than three months he had dictated 6,000 lines of text—James O’Donnell suggests he made the count for payment to his scribes.

Besides all the scribal payments, there was the costly material of which books were made. To form double-ply sheets from the papyrus plant was labor intensive, from cutting to cross-laying to drying.

Even more difficult was the skinning, stretching, scraping, and drying of sheep or calf or goat skin to make parchment.

And copyists had to keep the sheet numbers in order if they wrote the text before the sheaves (quires) were bound into a codex.

Augustine had to be serviced by a literary industrial complex in order to produce the amazing number of his books.