The article which introduced me to the idea that Ancient Romans used ceramic discs for wiping: https://www.dailymail.co.uk/sciencetech/article-2264464/They-bit-scratchy-The-ceramic-gaming-pieces-new-research-claims-Roman-equivalent-loo-roll.html
The scholarly article that found mineralized feces on some ceramic discs from a Roman site: Charlier, Philippe & Brun, Luc & Pretre, Clarisse & Huynh-Charlier, Isabelle. (2012). CHRISTMAS 2012: Toilet hygiene in the classical era. BMJ (Clinical research ed.) 345. e8287. 10.1136/bmj.e8287.
Amazon Affiliate link to some planter pot saucers which I have put to a similar purpose: https://amzn.to/2QrLv9q (These would make a fantastic prank gift if wrapped as a white cylinder and labeled as "Roman Toilet Paper.")
An article on the mysterious repurposed ceramic discs found in some Native American archeological sites (Game pieces, or possibly used for the same purpose?): https://www.peachstatearchaeologicalsociety.org/index.php/22-game-stones/145-ceramic-discoidals