An ancient Roman central heating system – hot water would be flooded through the basement, and the floors would warm up. “Hypocaust” was the name of the system. This particular one, painted in 1884, was built in the city of Rottenburg am Neckar, which the Romans called Sumelocenna when they lived there. The city might have gotten its “rotten” name because of an earlier version of the word “rotten,” which also meant “ruined” – the Germans built their city over the ruins of the Roman settlement.
It took them a couple hundred more years before they started heating their floors again.