First off, I would say there's a pretty big chronological difference between "early civilization" and "the middle ages" — so you might want to be a bit careful about that! It's also not a rule breaking question at all, so you don't have to worry about being banned. I would propose the answer here is pretty simple—they didn't really consume pornography because it didn't really exist.

"But Brian" I hear you saying "I saw all these sexy marginalia!"The amusement of monks aside, I have answered this question in a variety of formats and variations over the years, but the general gist is to say, again, that pornography didn't exist as we would have thought of it then.

'Porn' as we know it is only about 150 years old! This is really surprising to most people, as they tend to think of the Karma Sutra and other things as pornography. But they're not, or at least in their original contexts they were not

“the explicit description or exhibition of sexual subjects or activity in literature, painting, films, etc., in a manner intended to stimulate erotic rather than aesthetic feelings” (OED)

Although pornography is a Greek word literally meaning “writers about prostitutes,” it is only found once in surviving Ancient Greek writing, where Arthenaeus comments on an artist that painted portraits of whores or courtesans. The word seemed to fall more or less out of use for fifteen hundred years until the first modern usage of the word (1857) to describe erotic wall paintings uncovered at Pompeii. I wouldn't really feel comfortable extending the earlier idea of obscenity/obscene libel into our idea of pornography until about 1750 or so.

This is not to say that erotic material did not exist, but that it was understood and treated differently. Often it circulated only in elite (especially male) audiences and it was quite alright in that format. Remember--only very highly educated (for the time) monks and nuns would have been looking at those texts. When the artist drew them, they would have known who their audience was and what was acceptable, and the viewer would have gotten a kick out of the--most likely.

The closest things to what you are describing are probably popular erotic songs that circulated through this era, or perhaps the fabliaux tradition. I have uploaded an example of one to imgur — it is a translation of "Du Prestre Ki Abevete" in John DuVal's PHD translation. You'll note that this is a very erotic, obscene, anti-clerical poem--but it is not pornography as we would understand it. (these are often amusing, but also often very misogynistic by our understandings.)

Nathaniel E Dubin has released a more recent (and fantastic) translation anthology, but I do not have access to it.

The Fabliaux are a bit beyond my usual realm, though I have been enjoying Lisa Perfetti's 2003 book Women and Laughter In Medieval Comic Literature where she argues that they are useful documents for understanding gender. However, it is a bit beyond my expertise, so I will defer to someone else to talk more about them and leave you with a little bit from Perfetti:

This debate on the “woman on top” topos is nowhere more evident than in the scholarship on the short rhymed comic tales called fabliaux. Early scholars of the genre, who tended to see the fabliaux as realistic reflections of everyday urban life, asserted that the tales reflected medieval society’s hatred of women.39 Scholars now recognize the danger of viewing fabliaux as documents describing actual social conditions in the Middle Ages, but there is nonetheless significant disagreement as to what such literary portrayals of feminine misrule might mean. While some argue that fabliaux are meant to condemn women because they portray them as deceitful, libidinous, and quarrelsome, others assert that fabliaux show admiration for the woman on top, who impresses us with her ingenuity, making the man, usually her husband, look ridiculous.

In conclusion though, these are special and significant texts that tell us a lot about sexuality--but they are not pornographic.