The great and highly advanced Roman waterway system known as the Aqueducts, are among the greatest achievements in the ancient world. The running water, indoor plumbing and sewer system carrying away disease from the population within the Empire wasn't surpassed in capability until very modern times. The Aqueducts, being the most visible and glorious piece of the ancient water system, stand as a testament to Roman engineering. Some of these ancient structures are still in use today in various capacities.
The aqueducts were built from a combination of stone, brick and the special volcanic cement pozzuolana. While their visible remains leave a definite impression, the great bulk of the Roman waterway system ran below ground. Channels bored through rock, or dug below the surface carried water where it was convenient and possible. Of the approximately 260 miles in the aqueduct system, only 30 miles consisted of the visible, mammoth arched structures.
The aqueducts were built only to carry the flow of water in areas where digging, burrowing, or surface grades presented problems, such as valleys. The entire system relied upon various gradients and the use of gravity to maintain a continuous flow; and the engineering at the time was remarkable. Without the aqueducts it would've been impossible to maintain the flow of water at the proper grades required.
When water reached Rome it flowed into enormous cisterns (castella) maintained on the highest ground. These large reservoirs held the water supply for the city and were connected to a vast network of lead pipes. Everything from public fountains, baths and private villas could tap into the network, sometimes provided a fee was paid. The water system was as politically motivated as any other massive public works project. Providing additional sources of incoming flow, feeding the baths or simply providing water access to more of the populace could grant great prestige.
Maintenance of the water system was a continuous task, and the Romans assigned a Curator Aquarum to oversee this undertaking. Paid laborers, slaves and the legions all had parts in building parts of the water system. The Curator Aquarum maintained the aqueducts of Rome, while similar curators oversaw those in the provinces. The legions however, when building new colonies or forts, were responsible for providing their own water supply. Just as they were the great road builders of the Empire, they most assuredly took part in the aqueduct construction of outlying areas.
11 separate aqueducts supplied the city of Rome and were built over a span of 500 years. The first, the Aqua Appia, was built in conjunction with the great southern road the Via Appia in 312 BC. Aqua Novus stretched the farthest from the city, reaching approximately 59 miles away. At its largest extant, nearly 200 cities within the empire were supplied buy aqueducts, far surpassing the capability of any civilization before or after for nearly another 2 millenia. The last Roman aqueduct built was the Aqua Alexandrina built in 226 AD.
In the waning days of the western empire, invading Germanic tribes cut the supply of water into Rome and only the Aqua Virgo, which ran completely underground, continued to deliver water. During the middle ages, a couple of the lines were restored, but full access to running water wasn't re-established until the Renaissance. At the height of the ancient city's population of approximately 1,000,000 inhabitants, the water system was capable of delivering up to 1 cubic meter of water per person in the city, more than what is commonly available in most cities today.