Aqueducts of Ancient Rome: From Aqua Appia to Aqua Claudia

The aqueducts of ancient Rome were a network of eleven channels, built between 312 BC and AD 226, that carried water by gravity from springs and rivers in the hills around the city. Beginning with the modest Aqua Appia and culminating in the towering arcades of the Aqua Claudia, they supplied public fountains, baths and private houses on a scale unmatched in Europe until modern times. Their remains, and the records of the official Frontinus, make them one of the best-documented engineering achievements of antiquity.

Why Rome needed aqueducts

For its first centuries Rome drew water from the Tiber, from wells and from springs on its hills. As the city grew in the 4th century BC, these sources became inadequate and often polluted. Rome already had large-scale drainage in the Cloaca Maxima, but it lacked a reliable supply of clean water.

Aqueducts solved this by tapping springs in the Sabine and Alban hills and the Anio valley, often tens of kilometres away. Water arrived continuously, day and night, and most of it flowed through public fountains and baths before running into the drains, helping to flush the sewers.

The eleven aqueducts

The aqueducts were built over more than five centuries, each named after its source or builder.

Lengths are rounded modern conversions of Frontinus’s figures or later estimates. Together the aqueducts ran for roughly 800 km.

Building the network

Republican beginnings

The Aqua Appia was begun in 312 BC by the censor Appius Claudius Caecus, who in the same year started the Via Appia. It ran almost entirely underground and entered the city at low level.

The Anio Vetus (“old Anio”), begun in 272 BC, was paid for with spoils from the war against King Pyrrhus of Epirus. It drew water from the river Anio and was much larger, though the river water was often muddy.

The Aqua Marcia, built by the praetor Quintus Marcius Rex between 144 and 140 BC, was the longest of the Republican aqueducts. Its cold, clear spring water was considered the best in Rome. Unlike its predecessors, it arrived high enough to supply the Capitoline Hill.

Agrippa and Augustus

Under Augustus, Rome’s water supply was transformed. His close ally Marcus Agrippa, serving as aedile in 33 BC at his own expense, repaired the older aqueducts, built the Aqua Julia and added hundreds of basins and fountains. In 19 BC he opened the Aqua Virgo, whose route avoided the hills by entering Rome from the north to supply his new baths on the Campus Martius.

Agrippa kept a trained gang of about 240 slaves to maintain the system. On his death in 12 BC they passed to Augustus, who gave them to the state. In 11 BC a permanent board of water commissioners, the cura aquarum, was created. Augustus also built the Aqua Alsietina, whose poor-quality lake water mainly served his artificial lake for staged naval battles.

The great imperial aqueducts

The emperor Caligula began two new aqueducts in AD 38, and Claudius completed them in AD 52. The Aqua Claudia brought spring water, while the Anio Novus (“new Anio”), the longest of all, drew from the river Anio. For their last stretch the two shared a single line of arches, with the Anio Novus channel above the Claudia, reaching heights of up to about 28 metres.

Where they crossed the Via Praenestina and Via Labicana, Claudius built a monumental double arch, later incorporated into the Aurelian Walls as the Porta Maggiore. Its inscriptions still record the work of Claudius and later repairs by Vespasian and Titus. Pliny the Elder wrote that nothing in the whole world was more remarkable than this supply of water.

Trajan’s Aqua Traiana of AD 109 served the Janiculum and the districts across the Tiber, and later powered grain mills on the hill. The last, the Aqua Alexandrina of AD 226, supplied the baths of Severus Alexander on the Campus Martius.

How they were engineered

Roman aqueducts relied entirely on gravity. Surveyors used levelling instruments such as the chorobates, a long table with a water groove, to lay out a channel that fell steadily from source to city. Gradients were often very gentle, sometimes less than a metre per kilometre.

Most of each aqueduct ran underground in a masonry channel called the specus, roofed with slabs or a vault and lined with waterproof mortar. Tunnels pierced hills, with vertical shafts every so often for access and ventilation. Only on the final approach across the low Campagna did the channels rise onto arcades, to arrive high enough to feed the city’s hills. Elsewhere in the empire, engineers built more spectacular bridges, such as the Pont du Gard in southern France and the Aqueduct of Segovia in Spain.

Builders used stone, brick and Roman concrete. Along the route, settling tanks (piscinae limariae) allowed silt to drop out. Hard water left thick calcium carbonate deposits that crews had to chip away.

Distribution in the city

Inside Rome, each aqueduct ended in a main distribution tank, the castellum, from which water flowed through lead pipes (fistulae) and terracotta channels to smaller tanks around the city. Frontinus divides the supply among imperial buildings, public works, public fountains (lacus) and private grants.

Most Romans collected water from street fountains, which ran continuously. Private connections were a privilege granted by the emperor, and the size of each pipe was regulated with a stamped bronze nozzle (calix). Frontinus complained of fraud: officials and plumbers illegally tapping pipes, fitting larger nozzles or selling water.

Lead pipes have led to claims that the Romans were poisoned by their water. Because Rome’s water was hard and flowing constantly, mineral deposits lined the pipes and limited contact with the lead; most scholars think aqueduct water was not a major source of lead poisoning, although exposure from other sources was significant.

Frontinus and administration

The best source on the system is Sextus Julius Frontinus, appointed water commissioner (curator aquarum) in AD 97 under the emperor Nerva. His treatise De aquis urbis Romae describes each aqueduct’s history, length, source and capacity, and explains how the system was managed and abused. He noted that the imperial maintenance staff, a gang of about 460 slaves added by Claudius alongside the older state gang, had often been diverted to private work.

Frontinus measured flows in a unit called the quinaria, based on pipe diameter. Because the unit does not take speed of flow into account, converting his totals into modern figures is difficult. Modern estimates for the whole system range from about 500,000 to more than 1,000,000 cubic metres per day.

Decline and revival

The aqueducts were maintained into late antiquity. During the Gothic siege of Rome in AD 537, the Ostrogothic king Vitiges cut the aqueducts, and the city’s population, already shrinking, came to rely again on the Tiber and wells. Some channels were patched in the early Middle Ages, but most fell out of use.

From the 15th century the popes restored Rome’s water supply. The Aqua Virgo was repaired and, as the Acqua Vergine, fed new fountains culminating in the Trevi Fountain, completed in 1762. Sixtus V built the Acqua Felice in 1586, partly along the line of the Aqua Alexandrina, and Paul V opened the Acqua Paola in 1612, reusing the sources of the Aqua Traiana.

Remains today

The most dramatic surviving arches stand in the Parco degli Acquedotti in south-east Rome, where the arcades of the Aqua Claudia stride across open fields alongside the later Acqua Felice. Sections of the Aqua Marcia, Tepula and Julia survive at Porta Tiburtina, and the arches of the Claudia continue across the city towards the Caelian and Palatine Hills.

Timeline

• 312 BC: Aqua Appia built by Appius Claudius Caecus.
• 272-269 BC: Anio Vetus built with spoils of the war against Pyrrhus.
• 144-140 BC: Aqua Marcia built by Quintus Marcius Rex.
• 33 BC: Agrippa, as aedile, repairs the system and builds the Aqua Julia.
• 19 BC: Aqua Virgo opened.
• 11 BC: Permanent water board (cura aquarum) established.
• AD 52: Claudius completes the Aqua Claudia and Anio Novus.
• AD 97: Frontinus becomes water commissioner and writes his treatise.
• AD 226: Aqua Alexandrina, the last ancient aqueduct, completed.
• AD 537: The Goths cut the aqueducts during the siege of Rome.

Why it matters

Rome’s aqueducts made possible a city of perhaps a million people, with public baths and fountains open to all. They show Roman engineering, public finance and administration working together on a vast scale, and they remain the model for the long-distance water supplies of modern cities.