Planning

State or privately constructed aqueducts were protected and regulated by law. Any proposed aqueduct had to be subjected to the scrutiny of civil authorities. Permission—from the senate or local authorities—was only granted if the proposal respected the water rights of other citizens; In general, Roman communities were concerned with allocating shared water resources according to need.[19] The land on which a state-financed aqueduct was built could be state land (ager publicus) or private property, but in either case it was subject to use and encroachment restrictions that could damage the fabric of the aqueduct. Therefore, state-funded aqueducts reserved a wide corridor of earth, up to 15 feet on each side of the outside of the aqueduct. Plowing, planting and construction were prohibited within this boundary. This regulation was necessary for the long-term integrity and maintenance of the aqueduct, but was not always easily accepted or enforced at the local level, especially when it was publicly considered common property. Some small municipal or privately built aqueducts may have required less strict and formal arrangements.[20]​.

Water springs and topography

Natural springs were by far the most common way to get water for aqueducts; For example, most of Rome's supply came from a few natural springs in the Anio Valley and its highlands. The water from the natural springs fed a stone or concrete fountain, and then entered the aqueduct conduit. Scattered canals will require several branches of conduits converging into one main one. Some systems drew water from open reservoirs, such as the two—still in use—that supplied water to the aqueduct of the provincial city of Augusta Emerita.[21]​.

The territory over which the aqueduct was to pass was carefully studied to ensure that the water flowed at an acceptable gradient for the entire route.[22] Roman engineers used various framing tools to trace the course of the aqueducts through the landscape. Checking horizontal levels with a chorobate, a flat wooden frame with a water level. Courses and angles could be plotted and verified using a groma "Groma (measuring instrument)"), a relatively simple device that was probably later displaced by the more sophisticated dioptra, the precursor of the modern theodolite. In book VIII of his work De Architectura, Vitruvius describes the need to ensure a constant supply, methods of prospecting and testing of drinking water.

Health issues

Greek and Roman doctors knew of the association between stagnant or contaminated water and waterborne diseases. They were also aware of the harmful health effects of lead, among miners and those who had to process it, and for this reason, ceramic pipes were preferred over lead. When lead pipes were used, a continuous flow of water and the inevitable deposition of waterborne minerals within the pipes gradually reduced soluble lead contamination of the water.[23]​ However, the level of lead in this water was 100 times higher than in water from local sources.[24]​.

Pipes and gradients

Most Roman aqueducts were flat-bottomed, arch-section conduits running below the ground surface, with inspection and access covers at regular intervals. Conduits above ground level were usually covered by slabs. The first conduits were built from carved stone ashlars, but from the late Republican era onwards, brick and concrete were often used. Concrete used for duct linings is usually waterproof. The flow of water depended solely on gravity. The volume of water transported within the conduit depended on the catchment hydrology (rainfall, absorption and runoff), the cross section of the conduit and its gradient; most pipes were about two-thirds full. The cross section of the duct was also determined by maintenance requirements; Workers had to be able to enter and access the complex, with minimal interruption to the general network.[26]​.

Vitruvius recommends a small gradient, a ratio of 1:4800 for the canal, presumably to prevent damage to the structure through erosion and water pressure. This value closely matches the measured gradients of the surviving masonry aqueducts. The gradient of the Gard bridge is 34 cm per km, with a vertical difference of 17 m over its entire length of 50 km: it could transport up to 20,000 cubic meters of water per day. The gradients of temporary aqueducts used for hydraulic mining could be considerably larger, such as Dolaucothi in Wales (with a maximum gradient of approximately 1:700) and Las Médulas in northern Hispania. When strong gradients were unavoidable in permanent conduits, the channel could be lowered by widening it or discharging it into a receiving tank to disperse the water flow and reduce its abrasive force.[27]​ The use of stepped waterfalls also helped to oxygenate the water and thus "refresh" it.[28]​.

Bridges and siphons

Some aqueduct conduits were supported along the valleys on arches of masonry, brick or concrete; The Pont du Gard, one of the most impressive surviving examples of a massive multi-spring conduit, spanned the valley of the River Gardon some 48.8 m (160 m) above Gardon itself. When they had to cross deep and long depressions, inverted siphons could be used instead of supports with arches; The conduit fed the water to a header tank, which supplied it to the pipes. The pipes crossed the valley at a lower level, supported by a "belly" bridge, and were then raised to a receiving tank at a slightly lower elevation. It was then discharged into another pipe; maintaining the global gradient. Siphon pipes were usually made of soldered lead, sometimes reinforced with concrete coatings or stone sleeves. Less often, the pipes were made of stone or ceramic, jointed as male-female and sealed with lead.[29]​.

Vitruvius describes the construction of siphons and the problems of blocking, blowing and ventilation at their lowest levels, where the pressures were greatest. However, siphons were versatile and effective if well constructed and well maintained. A horizontal section of high-pressure siphon tubes in the Gier Aqueduct bypassed the construction of bridges so that the river could remain navigable, using new parallel lead pipes, embedded in concrete.[30][31] Modern hydraulic engineers use similar techniques that allow collectors and water pipes to pass through depressions. In Arles, a minor branch of the main aqueduct supplied a local suburb via a lead siphon, the "belly" of which passed through a riverbed, eliminating any need to build a bridge.[32]

Inspection and maintenance

Roman aqueducts required a comprehensive system of regular maintenance. The "transparent corridors" created to protect the network of underground conduits, which were regularly for plows, plantations, roads and illegal buildings. Frontino describes penetration of the conduits by roots as particularly harmful.[33] The aqueduct conduits would have been regularly inspected and maintained by work patrols, to reduce algal encrustations, repair accidental breaches, clear the conduits of gravel and other loose debris, and remove calcium carbonate accretions in systems fed by hard water sources. Inspection and access points were provided at regular intervals in standard and buried conduits. Accretions inside the siphons could drastically reduce flow levels, due to the already narrow diameter of their tubes. Some had sealed openings that could have been used as "rolling eyes", possibly using a traction device. In Rome, where hard water supplies were the norm, mains plumbing was loosely buried under road curbs, for easy access; The accumulation of calcium carbonate in these pipes necessitated their frequent replacement.[34]​.

The aqueducts were under the general attention and administration of a water commissioner, it was a high quality and high profile appointment. In 97, Frontinus served as both consul and curator aquarum, under Emperor Nerva.[35] Little is known about the daily work of the aqueduct maintenance teams. Under Emperor Claudius, Rome's contingent of imperial aquarii comprised an aquarum family of 700 people, both slaves and free, financed through a combination of taxes on imperial land and water. They were supervised by an imperial liberal, who held the position of procurator aquarium.[36] Their work was an endless routine of patrol, inspection and cleaning, punctuated by occasional emergencies. The complete shutdown of any aqueduct for service would have been a rare event, as brief as possible, with repairs preferably made when water demand was lowest, which was probably at night. The water supply could be shut off at its exit from the aqueduct when small or local repairs were needed, but substantial maintenance and repair of the conduit itself required total diversion of water at any point upstream or at the source itself.

Distribution

The aqueduct network could be tapped directly, but was normally fed into public distribution terminals, known as castella aquae, which supplied various branches of locks, generally through lead or ceramic pipes. Later, the offer could be further subdivided. Licensed and paying private users have been recorded, along with feeding pipes that allowed public water to be supplied to their private property: the larger the pipe, the greater the flow and the higher the rate. Manipulation and fraud to avoid or reduce payment were common; the methods included installing unauthorized outlets, additional outlets, and illegally lengthening lead pipes; any of which could involve bribery or the connivance of unscrupulous officials or aqueduct workers. Official pipes bore inscriptions with information about the pipe maker, its installer, and probably its subscriber and owner.[38] During the imperial era, the production of lead became an imperial monopoly and the granting of rights to obtain water for private use from state-financed aqueducts became an imperial privilege.[39][40]​.

La construcción de un acueducto exigía mucha capacidad y conocimientos a los ingenieros romanos. Ocasionalmente se sufrían problemas por la mala calidad del trabajo en proyectos de gran envergadura, como atestiguó Sexto Julio Frontino, oficial jefe de los

recursos acuíferos de la ciudad de Roma, quien escribió:.

Cost

Considering the amount of surveying, underground construction and tiling required, a construction the size of an aqueduct could not be built in one go. Therefore, the engineers divided the entire construction into separate zones. Thanks to archaeological research, the borders of these construction zones have been determined. By an aqueduct 15,000 Roman feet long (4,400 modern m). It has also been shown that the surveying was carried out independently of the construction, which is currently the norm in large construction projects.

For each meter of aqueduct they had to excavate approximately 3 to 4 m³ of earth, followed by 1.5 m³ of concrete and brick, plus 2.2 m³ of sealing with plaster. The complete cost in labor is estimated at about 475,000 man-days, which with about 180 possible days of construction per year, depending on weather conditions, would mean that about 2,500 workers would have needed 16 months to complete it. The actual execution time seems to have been even longer, since this estimate obviates the problems of surveying and the production of construction materials. After construction, the ditches were filled in, the surface was flattened and a maintenance road was built. This road also served to delimit the areas in which agriculture was not allowed. Most Roman aqueducts have facilities of this type. The aqueduct to Lyon (the Lugdunum of Gaul Lugdunense) was marked with the following inscription:

Surveying

After selecting a good location for the aqueduct, it was necessary to ensure a constant downward slope in its course. Using devices similar to modern levels, Roman engineers were able to maintain a slope as small as 0.1%, that is, one meter of drop for every kilometer of aqueduct. In addition to the slope, it was necessary that the various construction sections could be joined together, while still maintaining a constant downward slope.

Roman aqueduct builders made careful use of the natural slope of the land. If the construction of one segment ended up too high for the next, they built a small pond to reduce the fall of water.

Concreting

The concrete used in the aqueduct was a combination of lime, sand, stones and water. Boards were used to build a framework on which the concrete was pressed. Modern testing of concrete quality shows that it exceeds current standards. This particular type of concrete was called opus caementicium.[42]​.

Civic and domestic

Rome's first aqueduct (312 BC) discharged at very low pressure and at a more or less constant rate into the Boarium Forum the city's main trading center and livestock market, probably into a series of low-level troughs or cascading basins; the upper one for domestic use, the lower one for the livestock that was marketed there. Most Romans would have filled buckets and storage jars in the water basins of their dwellings; the better off would have sent slaves to perform the same task. The elevation of the drain was too low to offer any home or building in the city a direct supply; The overflow drained into Rome's main sewer, and from there into the Tiber. At this time, Rome had no public baths. The first were probably built in the following century, based on the precursors of neighboring Campania; A limited number of private baths and small public baths on street corners would have had a private water supply, but once aqueduct water was moved to the higher elevations of the city, large, well-equipped public baths were built throughout the city, and drinking water was supplied to public fountains at high pressure. Public baths and fountains became distinctive features of Roman civilization, and baths in particular became important social centers.[43]​[44]​.

Most urban Romans lived in multi-story apartment blocks (insulae). Some blocks offered water services, but only to tenants on the more expensive lower floors; the rest would have drawn free water from public fountains.[45]​.

Agriculture

Between 65 and 90% of the population of the Roman Empire was involved in some form of agricultural work. Farmers whose villas or farms were near a public aqueduct could extract, under license, a certain amount of water from the aqueduct for summer irrigation at a predetermined time; This was intended to limit the depletion of the water supply to users further down the slope, and to help ensure fair distribution among all, at a time when water was most needed and scarce. Water was possibly the most important variable in the agricultural economy of the Mediterranean world. The natural sources of water in Roman Italy—springs, streams, rivers, and lakes—were unevenly distributed across the land, and water tended to be scarce when it was needed most, during the hot, dry summer growing season. Columella recommends that every farm contain a spring, a stream or a river; but he recognizes that not all farms had it.[46]​.

Farmland without a reliable water source in the summer was virtually useless. During the growing season, the water demand of a “modest local” irrigation system could consume as much water as the city of Rome; and the livestock whose manure fertilized the fields had to be fed and watered all year round. At least some Roman landowners and farmers depended in part or wholly on aqueduct water for farming as their main or only source of income, but only the fraction of aqueduct water involved can be guessed at. More certainly, the creation of municipal and urban aqueducts brought with it a growth of the intensive suburban market and efficient agriculture of fragile and perishable products such as flowers - for perfumes and for party garlands -, vines, vegetables and garden fruits; and small animals such as pigs and chickens, near municipal and urban markets.[47]​.

A license fee for piped water on farmland could lead to increased productivity, cash income from the sale of surplus food, and an increase in the value of the land itself. In the countryside, permits to extract aqueduct water for irrigation were particularly difficult to obtain; the exercise and abuse of such rights were subject to several known disputes and court rulings, and at least one political campaign; at the beginning of the century BC. C. Cato the Elder tried to block all illegal rural outlets, especially those belonging to the landed elite - "Look how much he bought the land for, where he is channeling the water!" - during his tenure as censor. His attempt at reform proved impermanent at best. Although illegal canalization could be punished by confiscation of property, including illegally irrigated land and its products, this law appears to have never been used, and was probably unworkable; Food surpluses kept prices low. Grain shortages in particular could lead to famine and social unrest. Any practical solution must find a balance between the water needs of urban populations and grain producers, tax the profits of the latter, and ensure sufficient grain at a reasonable cost for the poor Romans and the army Cura annonae. Instead of trying to impose unproductive and probably unenforceable bans, authorities issued individual water concessions and licenses—although rarely in rural areas—and regulated water outlets, with varying success. In the 19th century, Pliny the Elder, like Cato, could fulminate against grain producers who continued to grow fat with the benefits of water and public land.[48]

Some landowners avoided those restrictions and entanglements by purchasing water access rights to distant springs, not necessarily on their own land. A few, of great wealth and status, built their own aqueducts to transport that water from the original source to the field or town; Mumius Niger Valerius Vegetus bought the rights to a spring and its water from his neighbor, and the access rights to an intervening land corridor, and then built an aqueduct of just under 10 kilometers, connecting the spring to his own villa. The Senate's permission for this "Aqua Vegetiana" was only given when the project seemed not to affect the water rights of other citizens.[49]​.

Industrial

Some aqueducts supplied water to industrial sites, usually through an open channel dug into the ground, lined with clay or covered with wood to reduce water loss. Most of these canals were designed to operate on the steep slopes that could supply the high volumes of water needed in mining operations. Water was used in hydraulic mining to strip overburden and expose ore through crushing, to fracture and wash metallic rock already heated and weakened by fire, and to power water wheel seals and trip hammers that crushed ore for processing. Evidence of such watercourses and machines has been found at the Dolaucothi gold mines in south-west Wales.[50][51]​.

Mining sites such as the Dolaucothi gold mines and Las Médulas in northwestern Spain show multiple aqueducts that fed water from local rivers to the head of the mine. The canals may have deteriorated quickly, or become redundant as nearby ore was depleted. Las Médulas shows at least seven of these aqueducts, and Dolaucothi at least five. At Dolaucothi, miners used holding tanks as well as holding tanks. silencing, and sluice gates to control the flow, as well as canals for the diversion of water supplies. The remaining traces (palimpsest "Palimpsest (geology)") of these canals allow the sequence of extraction to be deduced.

Several sites fed by various aqueducts have not yet been thoroughly explored or excavated, such as those at Longovicium, near Lanchester, south of Hadrian's Wall, where water supplies may have been used to power hammers for forging iron.

At Barbegal in Roman Gaul, a reservoir fed an aqueduct that drove a cascading series of 15 or 16 overloaded watermills, which ground flour for the Arles region. Similar arrangements, although on a smaller scale, have been found in Caesarea Maritima, Venafrum, and Roman-era Athens. Rome's Aqua Traiana ran a flour mill on the Janiculum, west of the Tiber. A mill in the basement of the Baths of Caracalla were powered by the aqueduct spill; this was just one of the city's many mills powered by aqueduct water, with or without official permission. A law of the century prohibited the illicit use of aqueduct water for grinding.[52]

During the fall of the Roman Empire, some aqueducts were deliberately destroyed by enemies, but more fell into disuse due to the deterioration of Roman infrastructure and lack of maintenance, such as the Eifel Aqueduct. The observations made by the Spanish Pedro Tafur, who visited Rome in 1436, attempt to explain misunderstandings of the very nature of Roman aqueducts:

During the Renaissance, the remains of the city's massive masonry aqueducts inspired architects, engineers, and their owners; Pope Nicholas V renovated the main canals of the Aqua Virgo in 1453.[54] Many aqueducts of the ancient Roman Empire remained in good condition. The century-old reconstruction of the Segovia aqueduct in Hispania shows progress compared to the Pont del Gard, using fewer arches of greater height, and greater economy in the use of raw materials. The skill of building aqueducts was not lost, especially the smaller canals and more models that were used to move water wheels. Most of these mills in Britain were developed in medieval times for the production of bread, and used methods similar to those developed by the Romans, with 'troughs' carrying water from local rivers and streams.

Contenido

Antes del desarrollo de la tecnología del acueducto, los romanos, como la mayoría de sus contemporáneos del mundo antiguo, se basaron en manantiales de agua locales, como acuíferos, complementadas por aguas subterráneas procedentes de pozos de propiedad privada o pública y para aguas de lluvia estacionales recogidas desde los tejados dentro de depósitos de almacenamiento o cisternas.[3]​ La dependencia de las comunidades antiguas sobre estos recursos hídricos restringía su crecimiento potencial. Los acueductos de Roma no eran inventos estrictamente romanos; sus ingenieros habían sido familiarizados con las tecnologías de gestión del agua de sus aliados etruscos y griegos, pero lo cierto es que alcanzaron un gran nivel. Las escorrentías del agua de los acueductos iba a parar al alcantarillado de ciudades y pueblos. A principios de la época imperial, los acueductos de la ciudad suministraban agua a una población de más de un millón de habitantes y el suministro de agua extra para los servicios públicos se había convertido en una parte fundamental de la vida romana.[4]​ El agua de los acueductos también se utilizaba para proveer villas, jardines ornamentales urbanos y suburbanos, jardines de mercado o fincas agrícolas, siendo esto último punto el núcleo de la economía y la riqueza de Roma.[5]​.

Aqueducts of Rome

Rome had several natural springs within its perimeter walls, but its groundwater was notoriously foul; The water of the Tiber River was greatly affected by pollution and waterborne diseases. The city's water demand had probably exceeded local supplies, when in 312 BC. C., the city's first aqueduct, Aqua Appia, was commissioned by the censor Appius Claudius the Blind. The Aqua Appia was one of the two great public projects of the time; the other was a military road between Rome and Capua, the first stage of the so-called Appian Way.[6] Both projects had significant strategic value, since the Third Samnite War had been underway for thirty years. The road allowed for rapid troop movements; and by design or fortunate coincidence, most of the Aqua Appia ran within a relatively safe buried conduit, which was fed by a water spring 16.4 km from Rome, with a drop of 10 meters supplying approximately 75,500 cubic meters of water each day to a fountain in Rome's beef market, the Forum Boario, one of the lowest public spaces in the city.[7]

A second aqueduct, the Aqua Vetus, was commissioned some forty years later, financed by treasures confiscated from Pyrrhus of Epirus.[8] Its flow was more than twice that of the Aqua Appia, and it entered the city in raised arches, supplying water to the highest parts of the city.[9]

In the year 145 BC. C., the city's demand for water had once again exceeded the possibilities of its combined supplies. An official commission found that the aqueduct pipes were very poorly maintained, the water was being exhausted due to leaks and illegal cuts. The praetor Quintus Marcius Rex "Quintus Marcius Rex (praetor)") restored them and introduced a third, "healthier" supply, the Aqua Marcia, the longest aqueduct in Rome and high enough to supply water to the Capitoline Hill. The works cost 180,000,000 sesterces and took two years to complete.[10] As demand grew even more, more aqueducts were built, including the Aqua Tepula in 127 BC. C. and the Aqua Julia in 33 BC. c.

Aqueduct construction programs reached their peak in the imperial era. The reign of Augustus promoted the construction of the Aqua Virgo and the short pipeline of the Aqua Alsietina that supplied the artificial lake of Trastevere with water for nautical fights to entertain the population. The Aqua Augusta complemented the Aqua Marcia with "water of excellent quality."[11] Emperor Caligula began two aqueducts, which were completed by his successor Claudius; the 69 km Aqua Claudia, which provided good quality water but failed on several occasions; and the Anio Novus, the highest of all Rome's aqueducts and one of the most reliable, but prone to muddy and discolored waters, especially after rain, despite the use of settling tanks.[12]​.

Most of Rome's aqueducts were taken from different water sources in the valley and highlands of the Anio, the present-day Aniene River, east of the Tiber. A complex set of aqueduct junctions, tributary feeders and distribution reservoirs supplied water to each part of the city. Trastevere, the region of the city west of the Tiber, was served mainly by extensions of the city's various eastern aqueducts, transported along the river by lead pipes buried in the beds of the river bridges, thus forming an inverted siphon. By closing this ribbed supply for routine repair and maintenance work, the "positively harmless" waters of the Aqua Alsietina were used to supply Trastevere's public fountains. The situation was finally improved when Emperor Trajan built the Aqua Traiana in 109, bringing clean water directly to Trastevere from aquifers near Lake Bracciano.[15]

At the end of the century, the city was supplied with water with eleven aqueducts financed by the state. The total combined length of the conduits is estimated to be between 780 and 800 kilometers, of which approximately 47 km ran above ground level, supported by masonry. About 1 million cubic meters (300 million gallons) were supplied per day: 126% of the water supply of the current city of Bangalore, with a population of 10 million.[16]​.

Aqueducts of the Roman Empire

Hundreds of similar aqueducts were built throughout the Roman Empire. Many of them have collapsed or been destroyed, but there are many portions intact. The Zaghouan Aqueduct has a length of 92.5 km. It was built in the century to supply Carthage (in modern-day Tunisia). Surviving water bridges include the Gard Bridge in Gaul and the Segovia Aqueduct in Hispania. The longest single conduit, in addition to 240 km, is associated with the Aqueduct of Valens of Constantinople, "The known system is at least two and a half times the length of the longest Roman aqueducts recorded in Carthage and Cologne, but perhaps more significantly represents one of the most outstanding topographical successes of any pre-industrial society." Rivaling in terms of length and possibly equal or superior in cost and complexity is the provincial Aqua Alsietina which supplied an entire region, containing at least eight cities, including the major ports of Naples and Miseno; The sea voyages of merchants and the Roman navy required abundant supplies of fresh water.[17]​[18]​.

Planning

State or privately constructed aqueducts were protected and regulated by law. Any proposed aqueduct had to be subjected to the scrutiny of civil authorities. Permission—from the senate or local authorities—was only granted if the proposal respected the water rights of other citizens; In general, Roman communities were concerned with allocating shared water resources according to need.[19] The land on which a state-financed aqueduct was built could be state land (ager publicus) or private property, but in either case it was subject to use and encroachment restrictions that could damage the fabric of the aqueduct. Therefore, state-funded aqueducts reserved a wide corridor of earth, up to 15 feet on each side of the outside of the aqueduct. Plowing, planting and construction were prohibited within this boundary. This regulation was necessary for the long-term integrity and maintenance of the aqueduct, but was not always easily accepted or enforced at the local level, especially when it was publicly considered common property. Some small municipal or privately built aqueducts may have required less strict and formal arrangements.[20]​.

Water springs and topography

Natural springs were by far the most common way to get water for aqueducts; For example, most of Rome's supply came from a few natural springs in the Anio Valley and its highlands. The water from the natural springs fed a stone or concrete fountain, and then entered the aqueduct conduit. Scattered canals will require several branches of conduits converging into one main one. Some systems drew water from open reservoirs, such as the two—still in use—that supplied water to the aqueduct of the provincial city of Augusta Emerita.[21]​.

The territory over which the aqueduct was to pass was carefully studied to ensure that the water flowed at an acceptable gradient for the entire route.[22] Roman engineers used various framing tools to trace the course of the aqueducts through the landscape. Checking horizontal levels with a chorobate, a flat wooden frame with a water level. Courses and angles could be plotted and verified using a groma "Groma (measuring instrument)"), a relatively simple device that was probably later displaced by the more sophisticated dioptra, the precursor of the modern theodolite. In book VIII of his work De Architectura, Vitruvius describes the need to ensure a constant supply, methods of prospecting and testing of drinking water.

Health issues

Greek and Roman doctors knew of the association between stagnant or contaminated water and waterborne diseases. They were also aware of the harmful health effects of lead, among miners and those who had to process it, and for this reason, ceramic pipes were preferred over lead. When lead pipes were used, a continuous flow of water and the inevitable deposition of waterborne minerals within the pipes gradually reduced soluble lead contamination of the water.[23]​ However, the level of lead in this water was 100 times higher than in water from local sources.[24]​.

Pipes and gradients

Most Roman aqueducts were flat-bottomed, arch-section conduits running below the ground surface, with inspection and access covers at regular intervals. Conduits above ground level were usually covered by slabs. The first conduits were built from carved stone ashlars, but from the late Republican era onwards, brick and concrete were often used. Concrete used for duct linings is usually waterproof. The flow of water depended solely on gravity. The volume of water transported within the conduit depended on the catchment hydrology (rainfall, absorption and runoff), the cross section of the conduit and its gradient; most pipes were about two-thirds full. The cross section of the duct was also determined by maintenance requirements; Workers had to be able to enter and access the complex, with minimal interruption to the general network.[26]​.

Vitruvius recommends a small gradient, a ratio of 1:4800 for the canal, presumably to prevent damage to the structure through erosion and water pressure. This value closely matches the measured gradients of the surviving masonry aqueducts. The gradient of the Gard bridge is 34 cm per km, with a vertical difference of 17 m over its entire length of 50 km: it could transport up to 20,000 cubic meters of water per day. The gradients of temporary aqueducts used for hydraulic mining could be considerably larger, such as Dolaucothi in Wales (with a maximum gradient of approximately 1:700) and Las Médulas in northern Hispania. When strong gradients were unavoidable in permanent conduits, the channel could be lowered by widening it or discharging it into a receiving tank to disperse the water flow and reduce its abrasive force.[27]​ The use of stepped waterfalls also helped to oxygenate the water and thus "refresh" it.[28]​.

Bridges and siphons

Some aqueduct conduits were supported along the valleys on arches of masonry, brick or concrete; The Pont du Gard, one of the most impressive surviving examples of a massive multi-spring conduit, spanned the valley of the River Gardon some 48.8 m (160 m) above Gardon itself. When they had to cross deep and long depressions, inverted siphons could be used instead of supports with arches; The conduit fed the water to a header tank, which supplied it to the pipes. The pipes crossed the valley at a lower level, supported by a "belly" bridge, and were then raised to a receiving tank at a slightly lower elevation. It was then discharged into another pipe; maintaining the global gradient. Siphon pipes were usually made of soldered lead, sometimes reinforced with concrete coatings or stone sleeves. Less often, the pipes were made of stone or ceramic, jointed as male-female and sealed with lead.[29]​.

Vitruvius describes the construction of siphons and the problems of blocking, blowing and ventilation at their lowest levels, where the pressures were greatest. However, siphons were versatile and effective if well constructed and well maintained. A horizontal section of high-pressure siphon tubes in the Gier Aqueduct bypassed the construction of bridges so that the river could remain navigable, using new parallel lead pipes, embedded in concrete.[30][31] Modern hydraulic engineers use similar techniques that allow collectors and water pipes to pass through depressions. In Arles, a minor branch of the main aqueduct supplied a local suburb via a lead siphon, the "belly" of which passed through a riverbed, eliminating any need to build a bridge.[32]

Inspection and maintenance

Roman aqueducts required a comprehensive system of regular maintenance. The "transparent corridors" created to protect the network of underground conduits, which were regularly for plows, plantations, roads and illegal buildings. Frontino describes penetration of the conduits by roots as particularly harmful.[33] The aqueduct conduits would have been regularly inspected and maintained by work patrols, to reduce algal encrustations, repair accidental breaches, clear the conduits of gravel and other loose debris, and remove calcium carbonate accretions in systems fed by hard water sources. Inspection and access points were provided at regular intervals in standard and buried conduits. Accretions inside the siphons could drastically reduce flow levels, due to the already narrow diameter of their tubes. Some had sealed openings that could have been used as "rolling eyes", possibly using a traction device. In Rome, where hard water supplies were the norm, mains plumbing was loosely buried under road curbs, for easy access; The accumulation of calcium carbonate in these pipes necessitated their frequent replacement.[34]​.

The aqueducts were under the general attention and administration of a water commissioner, it was a high quality and high profile appointment. In 97, Frontinus served as both consul and curator aquarum, under Emperor Nerva.[35] Little is known about the daily work of the aqueduct maintenance teams. Under Emperor Claudius, Rome's contingent of imperial aquarii comprised an aquarum family of 700 people, both slaves and free, financed through a combination of taxes on imperial land and water. They were supervised by an imperial liberal, who held the position of procurator aquarium.[36] Their work was an endless routine of patrol, inspection and cleaning, punctuated by occasional emergencies. The complete shutdown of any aqueduct for service would have been a rare event, as brief as possible, with repairs preferably made when water demand was lowest, which was probably at night. The water supply could be shut off at its exit from the aqueduct when small or local repairs were needed, but substantial maintenance and repair of the conduit itself required total diversion of water at any point upstream or at the source itself.

Distribution

The aqueduct network could be tapped directly, but was normally fed into public distribution terminals, known as castella aquae, which supplied various branches of locks, generally through lead or ceramic pipes. Later, the offer could be further subdivided. Licensed and paying private users have been recorded, along with feeding pipes that allowed public water to be supplied to their private property: the larger the pipe, the greater the flow and the higher the rate. Manipulation and fraud to avoid or reduce payment were common; the methods included installing unauthorized outlets, additional outlets, and illegally lengthening lead pipes; any of which could involve bribery or the connivance of unscrupulous officials or aqueduct workers. Official pipes bore inscriptions with information about the pipe maker, its installer, and probably its subscriber and owner.[38] During the imperial era, the production of lead became an imperial monopoly and the granting of rights to obtain water for private use from state-financed aqueducts became an imperial privilege.[39][40]​.

La construcción de un acueducto exigía mucha capacidad y conocimientos a los ingenieros romanos. Ocasionalmente se sufrían problemas por la mala calidad del trabajo en proyectos de gran envergadura, como atestiguó Sexto Julio Frontino, oficial jefe de los

recursos acuíferos de la ciudad de Roma, quien escribió:.

Cost

Considering the amount of surveying, underground construction and tiling required, a construction the size of an aqueduct could not be built in one go. Therefore, the engineers divided the entire construction into separate zones. Thanks to archaeological research, the borders of these construction zones have been determined. By an aqueduct 15,000 Roman feet long (4,400 modern m). It has also been shown that the surveying was carried out independently of the construction, which is currently the norm in large construction projects.

For each meter of aqueduct they had to excavate approximately 3 to 4 m³ of earth, followed by 1.5 m³ of concrete and brick, plus 2.2 m³ of sealing with plaster. The complete cost in labor is estimated at about 475,000 man-days, which with about 180 possible days of construction per year, depending on weather conditions, would mean that about 2,500 workers would have needed 16 months to complete it. The actual execution time seems to have been even longer, since this estimate obviates the problems of surveying and the production of construction materials. After construction, the ditches were filled in, the surface was flattened and a maintenance road was built. This road also served to delimit the areas in which agriculture was not allowed. Most Roman aqueducts have facilities of this type. The aqueduct to Lyon (the Lugdunum of Gaul Lugdunense) was marked with the following inscription:

Surveying

After selecting a good location for the aqueduct, it was necessary to ensure a constant downward slope in its course. Using devices similar to modern levels, Roman engineers were able to maintain a slope as small as 0.1%, that is, one meter of drop for every kilometer of aqueduct. In addition to the slope, it was necessary that the various construction sections could be joined together, while still maintaining a constant downward slope.

Roman aqueduct builders made careful use of the natural slope of the land. If the construction of one segment ended up too high for the next, they built a small pond to reduce the fall of water.

Concreting

The concrete used in the aqueduct was a combination of lime, sand, stones and water. Boards were used to build a framework on which the concrete was pressed. Modern testing of concrete quality shows that it exceeds current standards. This particular type of concrete was called opus caementicium.[42]​.

Civic and domestic

Rome's first aqueduct (312 BC) discharged at very low pressure and at a more or less constant rate into the Boarium Forum the city's main trading center and livestock market, probably into a series of low-level troughs or cascading basins; the upper one for domestic use, the lower one for the livestock that was marketed there. Most Romans would have filled buckets and storage jars in the water basins of their dwellings; the better off would have sent slaves to perform the same task. The elevation of the drain was too low to offer any home or building in the city a direct supply; The overflow drained into Rome's main sewer, and from there into the Tiber. At this time, Rome had no public baths. The first were probably built in the following century, based on the precursors of neighboring Campania; A limited number of private baths and small public baths on street corners would have had a private water supply, but once aqueduct water was moved to the higher elevations of the city, large, well-equipped public baths were built throughout the city, and drinking water was supplied to public fountains at high pressure. Public baths and fountains became distinctive features of Roman civilization, and baths in particular became important social centers.[43]​[44]​.

Most urban Romans lived in multi-story apartment blocks (insulae). Some blocks offered water services, but only to tenants on the more expensive lower floors; the rest would have drawn free water from public fountains.[45]​.

Agriculture

Between 65 and 90% of the population of the Roman Empire was involved in some form of agricultural work. Farmers whose villas or farms were near a public aqueduct could extract, under license, a certain amount of water from the aqueduct for summer irrigation at a predetermined time; This was intended to limit the depletion of the water supply to users further down the slope, and to help ensure fair distribution among all, at a time when water was most needed and scarce. Water was possibly the most important variable in the agricultural economy of the Mediterranean world. The natural sources of water in Roman Italy—springs, streams, rivers, and lakes—were unevenly distributed across the land, and water tended to be scarce when it was needed most, during the hot, dry summer growing season. Columella recommends that every farm contain a spring, a stream or a river; but he recognizes that not all farms had it.[46]​.

Farmland without a reliable water source in the summer was virtually useless. During the growing season, the water demand of a “modest local” irrigation system could consume as much water as the city of Rome; and the livestock whose manure fertilized the fields had to be fed and watered all year round. At least some Roman landowners and farmers depended in part or wholly on aqueduct water for farming as their main or only source of income, but only the fraction of aqueduct water involved can be guessed at. More certainly, the creation of municipal and urban aqueducts brought with it a growth of the intensive suburban market and efficient agriculture of fragile and perishable products such as flowers - for perfumes and for party garlands -, vines, vegetables and garden fruits; and small animals such as pigs and chickens, near municipal and urban markets.[47]​.

A license fee for piped water on farmland could lead to increased productivity, cash income from the sale of surplus food, and an increase in the value of the land itself. In the countryside, permits to extract aqueduct water for irrigation were particularly difficult to obtain; the exercise and abuse of such rights were subject to several known disputes and court rulings, and at least one political campaign; at the beginning of the century BC. C. Cato the Elder tried to block all illegal rural outlets, especially those belonging to the landed elite - "Look how much he bought the land for, where he is channeling the water!" - during his tenure as censor. His attempt at reform proved impermanent at best. Although illegal canalization could be punished by confiscation of property, including illegally irrigated land and its products, this law appears to have never been used, and was probably unworkable; Food surpluses kept prices low. Grain shortages in particular could lead to famine and social unrest. Any practical solution must find a balance between the water needs of urban populations and grain producers, tax the profits of the latter, and ensure sufficient grain at a reasonable cost for the poor Romans and the army Cura annonae. Instead of trying to impose unproductive and probably unenforceable bans, authorities issued individual water concessions and licenses—although rarely in rural areas—and regulated water outlets, with varying success. In the 19th century, Pliny the Elder, like Cato, could fulminate against grain producers who continued to grow fat with the benefits of water and public land.[48]

Some landowners avoided those restrictions and entanglements by purchasing water access rights to distant springs, not necessarily on their own land. A few, of great wealth and status, built their own aqueducts to transport that water from the original source to the field or town; Mumius Niger Valerius Vegetus bought the rights to a spring and its water from his neighbor, and the access rights to an intervening land corridor, and then built an aqueduct of just under 10 kilometers, connecting the spring to his own villa. The Senate's permission for this "Aqua Vegetiana" was only given when the project seemed not to affect the water rights of other citizens.[49]​.

Industrial

Some aqueducts supplied water to industrial sites, usually through an open channel dug into the ground, lined with clay or covered with wood to reduce water loss. Most of these canals were designed to operate on the steep slopes that could supply the high volumes of water needed in mining operations. Water was used in hydraulic mining to strip overburden and expose ore through crushing, to fracture and wash metallic rock already heated and weakened by fire, and to power water wheel seals and trip hammers that crushed ore for processing. Evidence of such watercourses and machines has been found at the Dolaucothi gold mines in south-west Wales.[50][51]​.

Mining sites such as the Dolaucothi gold mines and Las Médulas in northwestern Spain show multiple aqueducts that fed water from local rivers to the head of the mine. The canals may have deteriorated quickly, or become redundant as nearby ore was depleted. Las Médulas shows at least seven of these aqueducts, and Dolaucothi at least five. At Dolaucothi, miners used holding tanks as well as holding tanks. silencing, and sluice gates to control the flow, as well as canals for the diversion of water supplies. The remaining traces (palimpsest "Palimpsest (geology)") of these canals allow the sequence of extraction to be deduced.

Several sites fed by various aqueducts have not yet been thoroughly explored or excavated, such as those at Longovicium, near Lanchester, south of Hadrian's Wall, where water supplies may have been used to power hammers for forging iron.

At Barbegal in Roman Gaul, a reservoir fed an aqueduct that drove a cascading series of 15 or 16 overloaded watermills, which ground flour for the Arles region. Similar arrangements, although on a smaller scale, have been found in Caesarea Maritima, Venafrum, and Roman-era Athens. Rome's Aqua Traiana ran a flour mill on the Janiculum, west of the Tiber. A mill in the basement of the Baths of Caracalla were powered by the aqueduct spill; this was just one of the city's many mills powered by aqueduct water, with or without official permission. A law of the century prohibited the illicit use of aqueduct water for grinding.[52]

During the fall of the Roman Empire, some aqueducts were deliberately destroyed by enemies, but more fell into disuse due to the deterioration of Roman infrastructure and lack of maintenance, such as the Eifel Aqueduct. The observations made by the Spanish Pedro Tafur, who visited Rome in 1436, attempt to explain misunderstandings of the very nature of Roman aqueducts:

During the Renaissance, the remains of the city's massive masonry aqueducts inspired architects, engineers, and their owners; Pope Nicholas V renovated the main canals of the Aqua Virgo in 1453.[54] Many aqueducts of the ancient Roman Empire remained in good condition. The century-old reconstruction of the Segovia aqueduct in Hispania shows progress compared to the Pont del Gard, using fewer arches of greater height, and greater economy in the use of raw materials. The skill of building aqueducts was not lost, especially the smaller canals and more models that were used to move water wheels. Most of these mills in Britain were developed in medieval times for the production of bread, and used methods similar to those developed by the Romans, with 'troughs' carrying water from local rivers and streams.