Rome’s reputation for hydraulic sophistication rests almost entirely on what came in. The aqueducts are celebrated, documented, still standing in fragments across three continents. What went out receives less attention — which is itself a Roman attitude, one the city encoded in both its architecture and its social hierarchy. The removal of waste was essential, constant, and largely invisible, performed by people the Latin sources named only when something went wrong.

The Cloaca Maxima — the Great Drain — is among the oldest continuously functioning pieces of Roman infrastructure. Built initially in the sixth century BC to drain the marshy valley between the Capitoline and Palatine hills that would become the Roman Forum, it has been carrying water to the Tiber for over 2,600 years. Tourists floating on the Tiber can still see its outlet — a rounded arch of tufa stone nearly four meters high, set into the river embankment near the Forum Boarium — and the drain itself, though substantially rebuilt and extended over centuries, remains active as part of Rome’s modern sewer and stormwater system. It is one of the oldest pieces of civil engineering in continuous use anywhere in the world.