The Corpus Inscriptionum Latinarum is a behemoth publication spanning 17 volumes in about 70 parts that record about 180,000 Latin inscriptions from Roman times, ranging from official scripts to lowly graffiti hastily etched on the walls of toilets and brothels.
Graffiti from Pompeii has culled some of the juiciest morsels, showing us that, indeed, the art of graffiti is a lost one:
V.5 (just outside the Vesuvius gate); 6641: Defecator, may everything turn out okay so that you can leave this place
I.2.20 (Bar/Brothel of Innulus and Papilio); 3932: Weep, you girls. My penis has given you up. Now it penetrates men’s behinds. Goodbye, wondrous femininity!
VIII.2 (in the basilica); 1820: Chie, I hope your hemorrhoids rub together so much that they hurt worse than when they every have before!
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Previously on Neatorama: 10 Insulting Words You Should Know
Also, phallus-signs throughout Mediterranean cities directed sailors to brothels. No literacy was needed.