What Roman tax on urine became famous after Emperor Vespasian defended its revenue?

The Roman tax on urine associated with Emperor Vespasian was called vectigal urinae.

According to ancient accounts, urine collected from public urinals was valuable to Roman industries because it contained ammonia. Fullers used it to clean and process wool and clothing. The state therefore taxed its collection or sale, making an otherwise discarded substance part of the urban economy.

The story is linked to Emperor Vespasian, who ruled from 69 to 79 CE. When his son Titus objected to the unpleasant source of the revenue, Vespasian reportedly held a coin and asked whether it smelled. This produced the famous phrase pecunia non olet—“money does not stink.” The saying is widely quoted, although surviving accounts were written later and the precise administrative details are uncertain.