Aqueducts: Quenching Rome’s Thirst (2024)

This story appears in the November/December 2016 issue of National Geographic History magazine.

Aqueducts: Quenching Rome’s Thirst (1)

Rome is known for many things: its military conquests, its civic architecture, temples, roads, emperors, and sculpture. Yet none of these would have been possible without the most vital resource of all: water. Now, as then, water is life, and without effective distribution, there would have been no great Roman civilization. Even until relatively modern times, Roman techniques to collect, store, and channel water over huge distances remained unsurpassed.

Such technology, was not, of course, invented from scratch by the Romans, and many earlier Mediterranean peoples had poured resources and expertise into managing water. On the island of Crete, the Minoans developed sophisticated rain-harvesting and filtering systems as early as the middle of the third millennium B.C. Cretan water management techniques were later adopted across the Greek-speaking world, and examples abound of tunnels, drainage systems, and cisterns, sometimes of considerable size.

Yet although the water management tradition Rome inherited was rich and extensive, no previous system came close to the sophistication and reach of the Roman aqueduct. Striding across the landscape from Spain to Syria, these awe-inspiring structures not only carried life and livelihood but also proclaimed the greatness of Rome.

Timeline: Bringing Water to Rome

Aqueducts: Quenching Rome’s Thirst (2)

312 B.C.
The censor Appius Claudius Caecus builds Rome’s first aqueduct, the Aqua Appia, which runs almost entirely underground.

144 B.C.
Work begins on Rome’s longest aqueduct, the 56-mile-long Aqua Marcia. The city has doubled in size since the last channel was built.

33 B.C.
After the chaotic civil wars Octavian (later Emperor Augustus) improves Rome’s water by building the Aqua Julia.

19 B.C.
Marcus Agrippa, Augustus’s son-in-law, oversees the building of the Aqua Virgo to supply the thermal baths in the Campus Martius.

A.D. 38-52
Caligula begins a new aqueduct to meet increased demand from baths. Claudius nishes the work and calls it Aqua Claudia.

A.D. 109
Trajan builds the Aqua Traiana, which brings water from near Lake Bracciano to supply Rome’s new suburbs, known today as Trastevere.

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The Lifeline of Empire

Aqueducts were costly public works, and not all Roman cities necessarily required them. Some cities, such as Pompeii, had their water needs met by wells or public and private cisterns dug beneath houses. Some cisterns could reach a colossal size, such as the Basilica Cistern (Yerebatan Sarnıcı) in Constantinople (now Istanbul, Turkey) and the Piscina Mirabilis in Miseno, Italy. The latter, built to provide drinking water to the Roman navy in the Bay of Naples, had a capacity of just under half a million cubic feet. Its colossal vault is held up by 48 pillars. Some cities needed much more water than cisterns could provide. Booming populations such as Rome’s—thought to have reached one million in the first century A.D.—needed an entire system of aqueducts not only for drinking water but also for supplying ornamental public fountains and baths.

The popular image many people have of an aqueduct is probably something like the spectacular bridge structure of the Pont du Gard in southern France. These aboveground arches were, in fact, only a small section of an aqueduct system. Roman engineers would create a gentle downward slope all the way from start to finish, since the only force powering the water’s progress was gravity. Only valleys or gullies necessitated a monumental arched structure. For most of its route, water ran along underground or ground-level channels. Rome, for example, was supplied by aqueducts totaling 315 miles in length. Of that, 269 miles ran underground and 46 total miles aboveground; however, only about 36 miles consisted of arched structures—just under 12 percent in all.

Digging Tunnels

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Most of an aqueduct’s course lay underground, along channels that required huge resources and manpower to build. Once the route had been designed, a series of shafts (putei) were dug at intervals of around 230 feet following an ancient Persian technique known as qanat. When the planned depth was reached, construction of the channel or specus began. The shafts were used to carry away dirt in baskets and send down building materials.

A crane was used to lower stone blocks, which may have been brought from a nearby quarry, to form the lining for the tunnel walls. Depending on the local availability of materials, bricks or concrete were sometimes used for this purpose. The channel was usually waterproofed with a layer of opus signinum, a kind of mortar made of fragments of crushed tiles and amphorae.

Working With Geography

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Roman piping systems carried water from sources to the city for dozens of miles. The route had to gently slope to allow gravity to carry the water to its destination. Engineers followed the land’s natural grade wherever possible, building channels underground—even if that meant having to make long detours. The Aqua Traiana was a total of 37 miles long, but the distance, as the crow flies, between the spring and Rome was about 31 miles. Only when they had no other choice—when they had to cross a valley or avoid a sudden drop—did they build the spectacular archways, sometimes several stories tall, that dominate the Mediterranean landscape.

1. Materials: Basic Roman construction materials were stone blocks, concrete, mortar, tiles, and bricks. The structure was faced with a mix of lime and crushed ceramic.

2. Scaffolding: As the construction process advanced, wooden scaffolding was built to aid the workmen, many of whom would have been slaves.

3. Centering: This wooden structure bore the arch’s weight until the last stone was laid. When it was removed, the slotted stones could support their own weight.

4. Arches: Bridges could have two or—less commonly—as many as three tiers of arches. Roman engineers opted for narrow arches, which provided maximum strength.

5. Pillars: Massive pillars, measuring around 10 feet by 10 feet, were required to bear the weight of the arch tiers, and were usually longer at the base of the structure.

6. Specus: The specus, or water channel, was on the top level of the viaduct and covered with a roof or vault. Sometimes two or more channels were laid on top of one another.

Keeping the Water Running

Rome had as many as 11 aqueduct systems, the most ancient of which was the mile-long Aqua Appia, first operational in 312 B.C. It was named for its sponsor, the censor Appius Claudius Caecus, better known for another great pioneering structure of ancient Rome: the Appian Way, one of the first major Roman roads.

Three more aqueducts were built in the third and second centuries B.C.: Aqua Anio Vetus, Aqua Marcia, and Aqua Tepula. Aided by his son-in-law Marcus Vipsanius Agrippa, Emperor Augustus was particularly active in improving the capital’s water supply, repairing old systems and building new ones. The Augustan-era Aqua Virgo—named, according to legend, for the young girl who directed thirsty soldiers to the springs that fed it—has been used uninterrupted ever since its construction. During his reign, Caligula began building two aqueducts that were finished by Emperor Claudius, the Aqua Claudia and Aqua Anio Novus. Trajan built the Aqua Traiana, which is 37 miles long, in A.D. 109. The last of Rome’s aqueducts was the Aqua Alexandrina, nearly 14 miles long, built by Alexander Severus in A.D. 226. Some have calculated that, once completed, Rome’s aqueducts delivered roughly 1.5 million cubic yards of water per day—about 200 gallons per person. Its water network supplied 11 grand-scale baths, as well as the 900 or so public baths, and almost 1,400 monumental fountains and private swimming pools.

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A crucial later stage in the conveying of water was, of course, its disposal. Rome’s Cloaca Maxima sewer, which flowed into the Tiber River, became the model for urban sanitation. By the time Pliny the Elder was writing in the first century A.D., the Cloaca was already ancient: “[F]or 700 years from the time of Tarquinius Priscus, the sewers have survived almost completely intact,” he notes admiringly in his encyclopedia Naturalis historia.

A Titanic Enterprise

From planning to completion, building an aqueduct was an extremely costly enterprise, a project for which many Roman cities proudly raised funds. Evidence shows that money often came from both public and private sources.

Sometimes aqueducts were paid for by leading citizens. The work was usually carried out as part of their political role. For example, as aedile and consul, Augustus’ son-in-law Agrippa used his own mines to produce the lead pipes that lined the Aqua Julia and Aqua Virgo. From Augustus’ time onward, emperors regularly made donations to the upkeep of this expensive infrastructure.

Among the very few sources to shed light on how aqueducts were built is a Roman funerary monument found at the city of Bejaïa in Algeria. This commemorates the life of one Nonius Datus, an engineer, and recounts the difficulties he encountered in carrying out his work. The long text, written after the aqueduct’s completion around A.D. 152, describes how the city’s inhabitants lobbied for an improved water supply. The process was not as speedy as might have been hoped. Datus planned the aqueduct’s route in around 138. However, the work was not completed until 152, following a series of setbacks, which the monument describes in detail. Most crucially, the teams of workmen who started excavating the two sides of the tunnel did not meet where they were supposed to. On another occasion, bandits attacked the site and Datus escaped by the skin of his teeth, naked, battered, and bruised.

The Roman administration expended huge efforts not just in conveying water, but in maintaining its purity. A large group of specialized workers known as aquarii, ensured the aqueducts’ proper operation and cleanliness. These technicians carried out repairs and systematically cleaned the channels to prevent blockages and maintain a decent water quality. The channel along which the water flowed was always kept covered and tanks called piscinae limariae were placed along the route into which impurities were regularly decanted.

Bridging Past and Present

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One of Roman Spain’s most iconic monuments, the Segovia aqueduct is a UNESCO World Heritage site, and one of the best preserved Roman aqueducts in the world. Built to carry water from the Frío River 10 miles away, the structure was traditionally attributed to the emperor Augustus. Recent studies have shown it dates from the period of the emperor Trajan in the first part of the second century A.D.

Known by Segovians as El Puente (“the bridge”), the aqueduct features 168 arches. In recent years basins have been found alongside the channel, originally built to filter out the sand carried along from its source. Unlike other aqueduct bridges, plundered for their stone, the Segovia structure has been in almost constant use since its construction, ensuring it has survived intact for nearly 2,000 years.

Aqueducts: Quenching Rome’s Thirst (7)

Siphoning Off

Even for Romans, private access to water came at a price. Homeowners who could afford running water paid for the service based on the diameter of their access pipe, a not entirely foolproof billing system. There are records of homeowners slyly installing wider pipes than those for which they paid. This scam led to the invention of the calix, a sleeved pipe fitted into the wall, which was decorated to prevent forgeries or alterations. They were also used in the castella aquarum, the tanks from which water was distributed to different parts of the city. Despite regulation, some Romans tried to steal water from the source and would drain off water from the aqueduct or bribe the aquarii to do so. In the first century A.D. the senator Sextus Julius Frontinus mentioned this practice in his treatise De aquaeductu as “fraus aquariorum”: plumbing fraud.

To such a practical people as the Romans, aqueducts were a source of great pride and even part of their identity. Frontinus made that clear in his treatise on these great public works. “With such an array of indispensable structures carrying so much water, compare, if you will, the idle Pyramids or the useless, though famous, works of the Greeks!”

Aqueducts: Quenching Rome’s Thirst (8)

Isabel Rodà is Professor of Archaeology at the Autonomous University of Barcelona, Spain.

Aqueducts: Quenching Rome’s Thirst (2024)

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