Cloaca Maxima: the "great sewer" in Rome.
The Cloaca Maxima ("greatest sewer") is one of the oldest monuments of Rome. It was built as a canal through the Forum Romanum in the sixth century BCE and its construction is generally attributed to king Tarquinius Priscus. In the second century BCE, the canal was covered, so it became an underground sewer. There were extensive repairs during the reign of the emperor Augustus, executed by his right-hand man Agrippa (33 BCE). I
t is often stated that the Cloaca Maxima is still in use; this is not untrue, but the whole truth is that only a trickle of water flows through the age-old sewer - or sewers, because there are actually seven of them.
The joint outfall is just south of the ancient Roman bridge now known as Ponte Rotto. Another place where it can be seem is at the eastern stairs of the Basilica Julia at the Roman Forum, where a door leads to the sewer. Here, you can sometimes hear (and smell) the water in the ancient sewer.
The underground structure was much praised. Here are the words of Pliny the Elder:
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.note[Pliny the Elder, National History 36.104-106; tr. J.F. Healy.]
On several places, monuments were placed over the sewer. For example, at the Forum Romanum, there was the small sanctuary of Venus Cloacina, in the southern stairs of the Basilica Aemilia. This sanctuary, which is indeed dedicated to "Venus of the Sewer", was not well understood by the Romans themselves. Another monument that was in some sense connected to the sewer was the Arch of Janus Quadrifrons. Its significance is again unknown, but the builders took care to erect this monument just on top of the cloaca.
The upper reaches of the Cloaca Maxima were under the Forum Transitorium and the Argiletum.