The Romans constructed aqueducts throughout their Republic and later Empire, to bring water from outside sources into cities and towns. Aqueduct water supplied public baths, latrines, fountains, and private households; it also supported mining operations, milling, farms, and gardens.
Aqueducts moved water through gravity alone, along a slight overall downward gradient within conduits of stone, brick, concrete or lead; the steeper the gradient, the faster the flow. Most conduits were buried beneath the ground and followed the contours of the terrain; obstructing peaks were circumvented or, less often, tunneled through. Where valleys or lowlands intervened, the conduit was carried on bridgework, or its contents fed into high-pressure lead, ceramic, or stone pipes and siphoned across. Most aqueduct systems included sedimentation tanks, which helped to reduce any water-borne debris. Sluices, castella aquae (distribution tanks) and stopcocks regulated the supply to individual destinations, and fresh overflow water could be temporarily stored in cisterns.
Aqueducts and their contents were protected by law and custom. The supply to public fountains took priority over the supply to public baths, and both took priority over supplies to wealthier, fee-paying private users. Some of the wealthiest citizens were given the right to a free supply, as a state honour. In cities and towns, clean run-off water from aqueducts supported high consumption industries such as fulling and dyeing, and industries that employed water but consumed almost none, such as milling. Used water and water surpluses fed ornamental and market gardens, and scoured the drains and public sewers. Unlicensed rural diversion of aqueduct water for agriculture was common during the growing season, but was seldom prosecuted as it helped keep food prices low; agriculture was the core of Rome's economy and wealth.Bannon, Cynthia. Gardens and Neighbors: Private Water Rights in Roman Italy. University of Michigan Press, 2009, pp. 65–73
Rome's first aqueduct was built in 312 BC, and supplied a water fountain at the city's cattle market. By the 3rd century AD, the city had eleven aqueducts, sustaining a population of over a million in a water-extravagant economy; most of the water supplied the city's many public baths. Cities and towns throughout the Roman Empire emulated this model, and funded aqueducts as objects of public interest and civic pride, "an expensive yet necessary luxury to which all could, and did, aspire".Gargarin, M. and Fantham, E. (editors). The Oxford Encyclopedia of Ancient Greece and Rome, Volume 1. p. 145. Most Roman aqueducts proved reliable and durable; some were maintained into the early modern era, and a few are still partly in use. Methods of aqueduct surveying and construction are noted by Vitruvius in his work De architectura (1st century BC). The general Frontinus gives more detail in his official report on the problems, uses and abuses of Imperial Rome's public water supply. Notable examples of aqueduct architecture include the supporting piers of the Aqueduct of Segovia, and the aqueduct-fed cisterns of Constantinople.
Background
Before the development of aqueduct technology, Romans, like most of their contemporaries in the ancient world, relied on local water sources such as springs and streams, supplemented by groundwater from privately or publicly owned wells, and by seasonal rain-water drained from rooftops into storage jars and cisterns.Mays, L. (editor). Ancient Water Technologies. Springer. 2010. pp. 115–116. Such localised sources for fresh water – especially wells – were intensively exploited by the Romans throughout their history, but reliance on the water resources of a small catchment area restricted the city's potential for growth and security. The water of the River Tiber was close at hand, but would have been polluted by water-borne disease. Rome's aqueducts were not strictly Roman inventions – their engineers would have been familiar with the water-management technologies of Rome's Etruscan and Greek allies – but they proved conspicuously successful. By the early Imperial era, the city's aqueducts helped support a population of over a million, and an extravagant water supply for public amenities had become a fundamental part of Roman life.Gargarin, M. and Fantham, E. (editors). The Oxford Encyclopedia of Ancient Greece and Rome, Volume 1. Oxford University Press. 2010. pp. 144–145.
Rome's aqueducts
The city's aqueducts and their dates of completion were: 312 BC Aqua Appia 272 BC Aqua Anio Vetus 144–140 BC Aqua Marcia 127–126 BC Aqua Tepula 33 BC Aqua Julia 19 BC Aqua Virgo 2 BC Aqua Alsietina 38–52 AD Aqua Claudia 38–52 AD Aqua Anio Novus 109 AD Aqua Traiana 226 AD Aqua Alexandrina
The city's demand for water had probably long exceeded its local supplies by 312 BC, when the city's first aqueduct, the Aqua Appia, was commissioned by the censor Appius Claudius Caecus. The Aqua Appia was one of two major public projects of the time; the other was a military road between Rome and Capua, the first leg of the so-called Appian Way. Both projects had significant strategic value, as the Third Samnite War had been under way for some thirty years by that point. The road allowed rapid troop movements; and by design or fortunate coincidence, most of the Aqua Appia ran within a buried conduit, relatively secure from attack. It was fed by a spring from Rome, and dropped over its length to discharge approximately of water each day into a fountain at Rome's cattle market, the Forum Boarium, one of the city's lowest-lying public spaces.
A second aqueduct, the Aqua Anio Vetus, was commissioned some forty years later, funded by treasures seized from Pyrrhus of Epirus. Its flow was more than twice that of the Aqua Appia, and supplied water to higher elevations of the city.
By 145 BC, the city had again outgrown its combined supplies. An official commission found the aqueduct conduits decayed, their water depleted by leakage and illegal tapping. The praetor Quintus Marcius Rex restored them, and introduced a third, "more wholesome" supply, the Aqua Marcia, Rome's longest aqueduct and high enough to supply the Capitoline Hill. As demand grew still further, more aqueducts were built, including the Aqua Tepula in 127 BC and the Aqua Julia in 33 BC.
Aqueduct building programmes in the city reached a peak in the Imperial Era; political credit and responsibility for provision of public water supplies passed from mutually competitive Republican political magnates to the emperors. Augustus' reign saw the building of the Aqua Virgo, and the short Aqua Alsietina. The latter supplied Trastevere with large quantities of non-potable water for its gardens and was used to create an artificial lake for staged sea-fights to entertain the populace. Another short Augustan aqueduct supplemented the Aqua Marcia with water of "excellent quality". The emperor Caligula added or began two aqueducts completed by his successor Claudius; the Aqua Claudia, which gave good quality water but failed on several occasions; and the Anio Novus, highest of all Rome's aqueducts and one of the most reliable but prone to muddy, discoloured waters, particularly after rain, despite its use of settling tanks.
Most of Rome's aqueducts drew on various springs in the valley and highlands of the Anio, the modern river Aniene, east of the Tiber. A complex system of aqueduct junctions, tributary feeds and distribution tanks supplied every part of the city. Trastevere, the city region west of the Tiber, was primarily served by extensions of several of the city's eastern aqueducts, carried across the river by lead pipes buried in the roadbed of the river bridges, thus forming an inverted siphon.Taylor, Rabun, M., (2002), Tiber River bridges and the development of the ancient city of Rome, pp. 16–17, accessed 22 June 2013 Whenever this cross-river supply had to be shut down for routine repair and maintenance works, the "positively unwholesome" waters of the Aqua Alsietina were used to supply Trastevere's public fountains. The situation was finally ameliorated when the emperor Trajan built the Aqua Traiana in 109 AD, bringing clean water directly to Trastavere from aquifers around Lake Bracciano.Hodge, A. Trevor, Roman Aqueducts and Water Supply, Duckworth Archaeology, 2002, pp. 255–256, and note 43.
By the late 3rd century AD, the city was supplied with water by eleven state-funded aqueducts. Their combined conduit length is estimated between , of which approximately were carried above ground level, on masonry supports. Most of Rome's water was carried by four of these: the Aqua Anio Vetus, the Aqua Marcia, the Aqua Claudia and the Aqua Anio Novus. Modern estimates of the city's supply, based on Frontinus' own calculations in the late 1st century, range from a high of per day to a more conservative per day, supplying an estimated population of .Brun, (1991) p. 99; Brun, (2013), pp. 306–307; population estimate, Carcopino, (1940), p. 18, cited in Brun, (1991).
Aqueducts in the Roman Empire
Hundreds of aqueducts were built throughout the Roman Empire. Many of them have since collapsed or been destroyed, but a number of intact portions remain. The Zaghouan Aqueduct, in length, was built in the 2nd century AD to supply Carthage (in modern Tunisia). Surviving provincial aqueduct bridges include the Pont du Gard in France and the Aqueduct of Segovia in Spain. The longest single conduit, at over , is associated with the Valens Aqueduct of Constantinople.Mango (1995) p. 17 "The known system is at least two and half times the length of the longest recorded Roman aqueducts at Carthage and Cologne, but perhaps more significantly it represents one of the most outstanding surveying achievements of any pre-industrial society".Jelena Bogdanovic, Crow, J., (team leader), Historical and Archaeological Context Constantinople and the longest Roman aqueduct Accessed August 28, 2016. Rivalling this in terms of length and possibly equaling or exceeding it in cost and complexity, is provincial Italy's Aqua Augusta. It supplied a great number of luxury coastal holiday-villas belonging to Rome's rich and powerful, several commercial fresh-water fisheries, market-gardens, vineyards and at least eight cities, including the major ports at Naples and Misenum; sea voyages by traders and Rome's Republican and Imperial navies required copious on-board supplies of fresh water.Da Feo, G., and Napoli, R. M. A., "Historical development of the Augustan Aqueduct in Southern Italy: twenty centuries of works from Serino to Naples", in: Water Science & Technology Water Supply, March 2007, pp. 131–133
Aqueducts were built to supply Roman military bases in Britain. The sites of permanent fortresses show traces of fountains and piped water, which were probably supplied by aqueducts from the Claudian period on. Permanent auxiliary forts were supplied by aqueducts from the Flavian period, possibly coincident with the regular demand for dependable water supplies by provincial military settlements equipped with bathhouses, once these were introduced.
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