The extraordinary greatness of the Roman Empire manifests itself above all in three things: the aqueducts, the paved roads, and the construction of the drains.
Dionysius of Halicarnassus, Ant. Rom. 3.67.5
The Cloaca Maxima, The underground system of drains and sewers lines, was the unseen marvel of Rome, worthy of literary commemoration. Pliny the Elder composed this dramatic paean to the Great Sewer:
Hills were tunneled into the course of the construction of the sewers, and Rome was a “city on stilts” beneath which men sailed when Marcus Agrippa was aedile. Seven rivers join together and rush headlong through Rome, and, like torrents, they necessarily sweep away everything in their path. With raging force, owing to the additional amount of rainwater, they shake the bottom and sides of the sewers.
Sometimes water from the Tiber flows backwards and makes its way up the sewers. Then the powerful flood-waters clash head-on in the confined space, but the unyielding structure holds firm. Huge blocks of stone are dragged across the surface above the tunnels; buildings collapse of their own accord or come crashing down because of fire; earth tremors shake the ground – but still, for seven hundred years from the time of Tarquinius Priscus, the sewers have survived almost completely intact (Natural History, 36).
Writing under the Empire, Livy described the system as one “for which the new magnificence of these days has scarcely been able to produce a match” (Ab Urbe Condita, I.52.6).
The Cloaca Maxima, begun by the last Etruscan king, Tarquinus Superbus, in the 6th century BC, was a canal designed to drain the marshy valleys that lay between the hills of Rome. By the time Frontinus had assumed the post of curator aquarum in A.D. 97, its concrete and masonry tunnels channeled rainwater and waste water used in the baths, fountains, and latrines and trash beneath the Fora and around the hills, and stood among extensive drainage networks in the valleys of the Circus Maximus and the Campus Martius. The joint exit is just south of the ancient Roman bridge now known as Ponte Rotto. One of the maintenance entrances to the system is found behind a door at the eastern stairs of the Basilica Julia at the Roman Forum. Parts of the Cloaca Maxima were still in use as sewers in the early 20th century.