Money has no smell
Vespasian taxed the urine collected from public latrines (urine is rich in ammonia, an industrial raw material of the day for fulling wool and tanning leather). When his son Titus found the tax distasteful, Vespasian took a coin of the revenue, held it to his son’s nose, and asked, "Does it smell?" Titus said no. "Yet it comes from urine." — "Pecunia non olet," money has no smell, became a Western proverb from then on. French to this day calls a public urinal a "vespasienne" (after Vespasian), a little joke of history.
Turning a lake into an amphitheatre
Nero’s "Golden House" covered a vast area, at whose center was an artificial lake — a private garden an emperor had dug for himself in the heart of the city, the most vivid symbol of tyranny. Vespasian ordered the lake drained and on the site built the Flavian Amphitheatre, holding fifty thousand. The choice of site was itself a statement: land a despot had taken for his own, given back to the Roman people as a place of public entertainment. He had died by the time the Colosseum was completed, and his son Titus opened it with a hundred days of games — a building that for two thousand years has been the very totem of the word "Rome."