The Emperor Vespasian decided he needed more income, but didn't feel raising the proportions of existing taxes was appropriate. So he instituted a new tax - on urine. Urine was, bizarrely enough, purchased for leatherworking and cleaning - it's the ammonia - so buyers had to pay a tax on urine sold that was collected from public lavatories from then on.

Vespasian's son, Titus, expressed disgust at the tax, but Vespasian is said to have waved a gold coin under his nose, and told him that the coin came from urine, yet it didn't smell. From which we get the modern Latin phrase 'Pecunia non olet' - 'Money doesn't smell'

Also, for this reason, some Romance languages still use words derived from Vespasian's name for urinals.