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Pont du Gard, France, a Roman era aqueduct circa 19 BC.

The ancient Romans typically constructed numerous aqueducts to serve any large city in their empire, as well as many small towns and industrial sites. The city of Rome itself, being the largest city, had the largest concentration of aqueducts, with water being supplied by eleven aqueducts constructed over a period of 500 years. Scholars can even predict the size of the city by its water supply. They served potable water and supplied the numerous baths and fountains in the city, as well as finally being emptied into the sewers, where they performed their last function in removing waste matter. The methods of construction are well described by Vitruvius in his work De Architectura written in the first century BC. His book would have been of great assistance to Frontinus, a general who was appointed in the late first century AD to administer the many aqueducts of Rome. He discovered a discrepancy between the intake and supply of water caused by illegal pipes inserted into the channels to divert the water, and reported on his efforts to improve and regulate the system to the emperor Trajan at the end of the first century AD. The report of his investigation is known as De aquaeductu. In addition to masonry aqueducts, the Romans built many more leats — channels excavated in the ground, usually with a clay lining. They could serve industrial sites such as gold mines, lead and tin mines, forges, water-mills and baths or thermae. Leats were very much cheaper than the masonry design, but all aqueducts required good surveying to ensure a regular and smooth flow of water.



The combined length of the aqueducts in the city of Rome is estimated between 420 and a little over 500 km. However, only 29 miles (47 km) were above ground, as most Roman aqueducts ran beneath the surface of the ground. Building underground helped to keep the water free from disease (the carcasses of animals would not be able to get into the aqueduct) and helped protect the aqueducts from enemy attack. The longest Roman aqueduct was that of Constantinople (Mango 1995). "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". Perhaps the second longest, the Zaghouan Aqueduct, is 57.5 miles (92.5 km) in length. It was built in the 2nd century to supply Carthage (in modern Tunisia).

Arches are often used to depict an aqueduct but should not be confused with the aqueduct itself. These arches, sometimes on several tiers, together with tunnels, were constructed to maintain the pitch of the aqueduct, and the flow of water, over irregular terrain, for the long course to its destination.

The water-carrying channel of the Tarragona Aqueduct

Roman aqueducts were extremely sophisticated constructions. They were built to remarkably fine tolerances, and of a technological standard that had a gradient (for example, at the Pont du Gard) of only 34 cm per km (3.4:10,000), descending only 17 m vertically in its entire length of 50 km (31 miles). The challenge of an aqueduct was to get this gradient right, because it will overflow or clot if not right. Powered entirely by gravity, they could carry large amounts of water very efficiently. The Pont du Gard could transport up to 20,000 cubic meters — nearly 6 million gallons — a day, and the combined aqueducts of the city of Rome supplied around 1 million cubic meters (300 million gallons) a day. These figures were however functions of the catchment hydrology and aqueduct regulation technique as shown by recent studies. (For comparison the maximum value represents a value 26% larger than the present water supply of the city of Bangalore, with a population of 6 million). Sometimes, where depressions deeper than 50m had to be crossed, gravity pressurized pipelines called inverted siphons were used to force water uphill (although they almost always used venter bridges as well). Modern hydraulic engineers use similar techniques to enable sewers and water pipes to cross depressions. In addition to the expertise needed to build them, Roman aqueducts required a comprehensive system of regular maintenance to repair accidental breaches, to clear the lines of debris, and to remove buildup of chemicals such as calcium carbonate that naturally occur in the water.

A portion of the Eifel aqueduct, Germany, built in AD 80, showing the calcium carbonate that accretes on the sides of the channel without regular maintenance.

The methods of building aqueducts and the surveying needed to ensure a regular water supply is described by Vitruvius in Book 8 of his De Architectura. The work specifies the tests needed to ensure that the water is potable, and he warns against lead pipes for their toxicity, recommending either masonry channels or clay pipes. He suggests a low gradient of not less than 1 in 4800 for the channel, presumably to prevent damage to the structure. This value agrees well with the measured gradients of surviving masonry aqueducts, but many temporary aqueducts, such as those used for gold mining, for example at Dolaucothi in Wales and Las Medulas in northern Spain, are much higher. At Dolaucothi, the gradient of the main 7 mile long structure is about 1:700, considerably higher than those of the permanent masonry aqueducts. Vitruvius also describes the construction of inverted siphons and the problems of blow-outs where the pressures were greatest. Aqueducts were built to supply water mills, the most famous excavated example being at Barbegal on the supply system for the Pont du Gard. The engineering here is impressive, with a single aqueduct driving 16 overshot mills linked together in series.

Construction of Roman aqueducts

Remains of aqueducts Aqua Claudia and Aqua Anio Novus, integrated into the Aurelian Wall as a gate in 271 AD.

The aqueducts required very careful planning before building, especially to determine the water source to be used, the length of aqueduct needed and its size. Great skill was needed to ensure a regular grade, so that the water would flow smoothly from its source without the flow damaging the walls of the channel. As the need for water grew, extra sources would be utilised, very often making use of existing structures as with the Aqua Claudia and Anio Novus in Rome. The problems of aqueduct building and use are described by Vitruvius and Frontinus, the latter producing a long report on the state of the Aqueducts of Rome in the last years of the first century AD.

Several surveying tools were used in the construction of Roman aqueducts, one example being the chorobates. The chorobates was used to level terrain before construction. It was a wooden frame supported by four legs with a flat board fitted with a water level and wooden arches to support the vaults. Another tool used in the construction of the aqueduct was the groma. Gromas were used to measure right angles. A groma consisted of stones hanging off four strings perpendicular to one another. The instrument which is the forerunner of the theodolite was known as the dioptra, and was used to measure vertical angles.

Industrial aqueducts

The aqueducts at Dolaucothi

Many houses were built to supply water to industrial sites, such as gold mines, where the water was used to prospect for or by hydraulic mining, and then crush and wash the ore to extract the gold. They usually consisted of an open channel dug into the ground, with a clay lining to prevent excessive loss of water and sometimes with wooden shuttering. They are often known as leats. However, they were built just as carefully as the masonry structures, but often at a higher gradient so as to deliver the greater volumes needed for mining operations.

Map of the gold mine

The large quantities of water supplied by the aqueducts were used for prospecting for ore-bodies by stripping away the overburden, and for working the ores in a method known as hushing. The technique was used in combination with fire-setting, which involved creating fires against the hard rock face to weaken the rock and so make removal much easier. These methods of mining survived into Medieval times until the widespread use of explosives. The water could also be used to wash ores, especially those of gold and tin, and probably to work simple machines such as ore-crushing hammers and water wheels.

The remains of such leats are visible today at sites like Dolaucothi in south-west Wales, and at Las Medulas in northwest Spain. These sites show multiple aqueducts, presumably because they were relatively short-lived and deteriorated rapidly. There are, for example, at least seven major leats at Las Medulas, and at least five at Dolaucothi feeding water from local rivers direct to the mine head. The palimpsest of such channels allows the mining sequence to be inferred.

Apparent Decline of Aqueducts

With the fall of the Roman Empire, although some of the aqueducts were deliberately cut by enemies, many more fell into disuse from the lack of an organized maintenance system. The decline of functioning aqueducts to deliver water had a large practical impact in reducing the population of the city of Rome from its high of over 1 million in ancient times to considerably less in the medieval era, reaching as low as 30,000. On the other hand, many others elsewhere in the empire continued in use, such as the aqueduct at Segovia in Spain, a construction which shows advances on the Pont du Gard by using fewer arches of greater height and so greater economy in its use of the raw materials. The skill in building aqueducts was not lost, especially of the smaller, more modest channels used to supply water wheels. Most such mills in Britain were developed in the medieval period for bread production, and used similar methods as that developed by the Romans with leats tapping local rivers and streams. The massive masonry aqueducts and the many other visible remains, such as the Pantheon, Coliseum, and Baths of Diocletian, were to inspire architects and engineers of the Renaissance.

See also


  • Bossy, G.; G. Fabre, Y. Glard, C. Joseph (2000). "Sur le Fonctionnement d'un Ouvrage de Grande Hydraulique Antique, l'Aqueduc de Nîmes et le Pont du Gard (Languedoc, France)" in Comptes Rendus de l'Académie des Sciences de Paris, Sciences de la Terre et des Planètes, Vol. 330, pp. 769–775.
  • Chanson, H. (2002). "Certains Aspects de la Conception hydrauliques des Aqueducs Romains", Journal La Houille Blanche, No. 6/7, pp. 43–57.
  • Chanson, H. (2008). "The Hydraulics of Roman Aqueducts: What do we know? Why should we learn ?" in Proceedings of World Environmental and Water Resources Congress 2008 Ahupua'a, ASCE-EWRI Education, Research and History Symposium, Hawaii, USA, Invited Keynote lecture, 13–16 May, R.W. Badcock Jr and R. Walton Eds., 16 pages (ISBN 978-0-7844-0976-3)
  • Coarelli, Filippo (1989). Guida Archeologica di Roma. Milano: Arnoldo Mondadori Editore.
  • Claridge, Amanda (1998). Rome: An Oxford Archaeological Guide. New York: Oxford University Press.
  • Fabre, G.; J. L. Fiches, J. L. Paillet (2000). L'Aqueduc de Nîmes et le Pont du Gard. Archéologie, Géosystème, Histoire, CRA Monographies Hors Série. Paris: CNRS Editions.
  • Gebara, C.; J. M. Michel, J. L. Guendon (2002). "L'Aqueduc Romain de Fréjus. Sa Description, son Histoire et son Environnement", Revue Achéologique de Narbonnaise, Supplément 33. Montpellier, France.
  • Hodge, A.T. (2001). Roman Aqueducts & Water Supply, 2nd ed. London: Duckworth.
  • Leveau, P. (1991). "Research on Roman Aqueducts in the Past Ten Years" in T. Hodge (ed.): Future Currents in Aqueduct Studies. Leeds, UK, pp. 149–162.
  • Lewis, P. R.; G. D. B. Jones (1970). "Roman gold-mining in north-west Spain", Journal of Roman Studies 60 : 169-85.
  • Lewis, P. R.; G. D. B. Jones (1969). "The Dolaucothi gold mines, I: the surface evidence", The Antiquaries Journal, 49, no. 2: 244-72.
  • Mango, Cyril (1995). "The Water Supply". in C. Mango, G. Dagron. Constantinople and Its Hinterland. Aldershot: Variorum. 
  • O'Connor, C. (1993). Roman Bridges, Cambridge: Cambridge University Press.

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