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.