Here's some history taken from the book...
"We don't know for sure what the first printed erotica was, although it certainly could not have predated the invention of the printing press in 1450. ... This [ie loss of single sheets and broadsides] should not surprise us, since even today a great amount of erotica - be it paperback books, privately issued posters or flyers or chap books, printed gimmicks and ephemera of all sorts - disappears without a trace on a daily basis."
And that's something that has changed in today's world with computers and the internet - it doesn't disappear. As much as some people would like it to, it's there forever.
"The earliest printed erotic work we have evidence for is the 1527 printing of Aretino's Sonnets, known in the original Italian as Sonetti Lussuriosi."
The book goes on to discuss the sonnets and their effect on society then and now (well, in the late 1980s).
This is the most remarkable thing about the classics (in literature and erotic literature) - their relevance still today, some 500 years later. How is that possible? How can people like Shakespeare, Arentino, John Cleland (author of Fanny Hill), Oscar Wilde, Charles Dickens, and The Marquis de Sade, have written something that remains relevant (sometimes even topical) many many years later? Were they gifted with foresight? Were they revolutionary? Or has humanity not changed that much?
I've got no answers, but feel free to offer some :) And do you think authors of today will be relevant 500 years from now, in 2513?