What ancient Roman sewer system drained the Roman Forum and still functions today?

The ancient Roman sewer system that drained the Roman Forum and still carries drainage today is the Cloaca Maxima.

Its earliest channel was probably developed during the Roman Kingdom, traditionally under the Tarquin kings in the sixth century BC. It helped drain marshy lowlands between Rome’s hills, making the valley suitable for the Roman Forum and other urban development. The system eventually carried water and waste toward the Tiber.

The Cloaca Maxima began as an open drainage channel and was gradually covered and enlarged. By the late Republic and imperial period, it formed part of a wider network serving streets, baths, public buildings, and storm-water drainage. Agrippa carried out major repairs and improvements in 33 BC.

“Still functions” does not mean the ancient system handles Rome’s entire modern sewage supply. Surviving sections remain connected to modern drainage infrastructure and continue to drain rainwater and runoff, especially around the Forum, Velabrum, and Forum Boarium. Circus Maximus is a racing venue, while Via Appia and Aqua Appia are roads or water infrastructure—not sewers.