One of the Pope's wrote an erotic book

Historia de duobus amantibus 
by Pope Prius II aka Aeneas Sylvius Piccolomini

Before he was Pope Pius II, Aeneas Sylvius Piccolomini was a poet, scholar, diplomat, and rakehell. And an author. In fact, he wrote a bestseller. Folks in fifteenth century Europe couldn't get enough of his Latin novella Historia de duobus amantibus. 

An article in a scholarly publication on literature claims that Historia de duobus amantibus "was undoubtedly one of the most read stories of

the whole Renaissance." The Oxford edition gives a Cliff Notes version of the storyline:

"The Goodli History tells of the illicit love of Euralius, a high official in the retinue of the [German] Emperor Sigismund, and Lucres, a married lady from Siena [Italy]." It was probably written in 1444, but the earliest known printing is from Antwerp in 1488. By the turn of the century, 37 editions had been published. Somewhere around 1553, the short book

appeared in English under the wonderfully old-school title The Goodli History of the Moste Noble and Beautyfull Ladye Lucres of Scene in Tuskane, and of Her Louer Eurialus Verye Pleasaunt and Delectable vnto ye Reder. 

Pope Pius II

Despite the obvious historical interest of this archaic Vatican porn, it has never been translated into contemporary language. (The passages quoted below mark the first time that any of the book has appeared in modern English.)

The 1400's being what they were, the action is pretty tame by today's standards. At one point, Euralius scales a wall to be with Lucres:

"When she saw her lover, she clasped him in her arms. There was embracing and kissing, and with full sail they followed their lusts and wearied Venus, now with Ceres, and now with Bacchus was refreshed." 

Loosely translated, that last part means that they shagged, then ate, then drank wine.

His Holiness describes the next time they hook up:

Thus talking to each other, they went into the bedroom, where they had such a night as we
judge the two lovers Paris and Helen had after he had taken her away, and it was so
pleasant that they thought Mars and Venus had never known such pleasure.... 

Her mouth, and now her eyes, and now her cheeks he kissed. Pulling down her clothes, he
saw such beauty as he had never seen before. "I have found more, I believe," said Euralius,
"than Acteon saw of Diana when she bathed in the fountain. What is more pleasant or
more fair than these limbs?... O fair neck and pleasant breasts, is it you that I touch? Is it
you that I have? Are you in my hands? O round limbs, O sweet body, do I have you in my
arms?... O pleasant kisses, O dear embraces, O sweet bites, no man alive is happier than I
am, or more blessed."... 

He strained, and she strained, and when they were done they weren't weary. Like Athens,
who rose from the ground stronger, soon after battle they were more desirous of war.
But Euralius isn't just a horndog. He waxes philosophical about love to Lucres' cousin-in-law:
You know that man is prone to love. Whether it is virtue or vice, it reigns everywhere. No
heart of flesh hasn't sometime felt the pricks of love. You know that neither the wise
Solomon nor the strong Sampson has escaped from this passion. Furthermore, the nature
of a kindled heart and a foolish love is this: The more it is allowed, the more it burns, with
nothing sooner healing this than the obtaining of the loved. There have been many, both in
our time and that of our elders, whose foolish love has been the cause of cruel death. And
many who, after sex and love vouchsafed, have stopped burning. Nothing is better when
love has crept into your bones than to give in to the burning, for those who strive against
the tempest often wreck, while those who drive with the storm escape.

Besides sex and wisdom, the story also contains a lot of humor, as when Lucres' husband borrows a horse from Euralius: "He says to himself, 'If you leap upon my horse, I shall do the same thing to your wife.'"

Popes just don't write books like that anymore!