Roman toilet paper: a sponge on a stick.
In Roman latrines, people sat side by side on long stone benches with holes. For cleaning they used a xylospongium, a sea sponge on a wooden stick, rinsed in vinegar or salt water and shared with the neighbours. The philosopher Seneca mentions it around AD 64; a 2nd-century inscription in a latrine at Ostia explicitly recommends using it.
Useful: When you imagine 'back then', include the things nobody wanted to write down.
Source: en.wikipedia.org