Primary Source: pliny the elder. http://www.masseiana.org/pliny.htm#BOOK XXXVI.
The Roman scholar Pliny, who lived from 23 A.D. to 79 A.D., was impressed with the Cloaca Maxima, and wrote about it in Natural History. Remarkably, during Pliny's lifetime, the Cloaca Maxima was already 700 years old (Pliny, Natural History). This same sewer that impressed Pliny is still in use today, almost 2000 years later.
In book XXXVI, section XXIV of Natural History, Pliny wrote:
"Through the city there flow seven rivers meeting in one channel. These, rushing
downwards like mountain torrents, are constrained to sweep away and remove
everything in their path, and when they are thrust forward by an additional
volume of rain water, they batter the bottom and sides of the sewers. Sometimes
the backwash of the Tiber floods the sewers and makes its way along them
upstream. Then the raging flood waters meet head on within the sewers, and even
so the unyielding strength of the fabric resists the strain. In the streets
above, massive blocks of stone are dragged along, and yet the tunnels do not
cave in. They are pounded by falling buildings, which collapse of their own
accord or are brought crashing to the ground by fire. The ground is shaken by
earth tremors; but in spite of all, for 700 years from the time of Tarquinius
Priscus, the channels have remained well-nigh impregnable. We should not fail
to mention an occasion that is all the more worthy of record because the
best-known historians have overlooked it. Tarquinius Priscus was carrying out
the work using the common folk as his labourers, and it became doubtful whether
the toil was to be more notable for its intensity or for its duration. Since
the citizens were seeking to escape from their exhaustion by committing suicide
wholesale, the king devised a strange remedy that was never contrived except on
that one occasion. He crucified the bodies of all who had died by their own
hands, leaving them to be gazed at by their fellow-citizens and also torn to
pieces by beasts and birds of prey. Consequently, the sense of shame, which is
so characteristic of the Romans as a nation and has so often restored a
desperate situation on the battlefield, then too came to their aid; but this
time it imposed upon them at the very moment when they blushed for their
honour, since they felt ashamed while alive under the illusion that they would
feel equally ashamed when dead. Tarquin is said to have made the tunnels large
enough to allow the passage of a waggon fully loaded with hay".
In book XXXVI, section XXIV of Natural History, Pliny wrote:
"Through the city there flow seven rivers meeting in one channel. These, rushing
downwards like mountain torrents, are constrained to sweep away and remove
everything in their path, and when they are thrust forward by an additional
volume of rain water, they batter the bottom and sides of the sewers. Sometimes
the backwash of the Tiber floods the sewers and makes its way along them
upstream. Then the raging flood waters meet head on within the sewers, and even
so the unyielding strength of the fabric resists the strain. In the streets
above, massive blocks of stone are dragged along, and yet the tunnels do not
cave in. They are pounded by falling buildings, which collapse of their own
accord or are brought crashing to the ground by fire. The ground is shaken by
earth tremors; but in spite of all, for 700 years from the time of Tarquinius
Priscus, the channels have remained well-nigh impregnable. We should not fail
to mention an occasion that is all the more worthy of record because the
best-known historians have overlooked it. Tarquinius Priscus was carrying out
the work using the common folk as his labourers, and it became doubtful whether
the toil was to be more notable for its intensity or for its duration. Since
the citizens were seeking to escape from their exhaustion by committing suicide
wholesale, the king devised a strange remedy that was never contrived except on
that one occasion. He crucified the bodies of all who had died by their own
hands, leaving them to be gazed at by their fellow-citizens and also torn to
pieces by beasts and birds of prey. Consequently, the sense of shame, which is
so characteristic of the Romans as a nation and has so often restored a
desperate situation on the battlefield, then too came to their aid; but this
time it imposed upon them at the very moment when they blushed for their
honour, since they felt ashamed while alive under the illusion that they would
feel equally ashamed when dead. Tarquin is said to have made the tunnels large
enough to allow the passage of a waggon fully loaded with hay".
Rackham, H., W.H.S. Jones, and D.E. Eichholz. "Pliny's Natural HIstory." Masseiana.org. Masseiana.org, n.d. Web. 19 Apr. 2013. http://www.masseiana.org/pliny.htm#BOOK XXXVI.
The greatest sewer continues
The Cloaca Maxima has outlasted the Roman Republic, the Roman Empire, many of the buildings which have been constructed above it, and thousands of generations of people living in Rome. The Cloaca Maxima is indeed the greatest sewer. Even now, it is quietly and steadfastly carrying out its duty, while tourists from around the world marvel at the ruins above.