Roman aqueduct

Sluices, castella aquae (distribution tanks) and stopcocks regulated the supply to individual destinations, and fresh overflow water could be temporarily stored in cisterns.

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".

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.

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.

[8] 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.

[14] "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".

State purchase of privately owned land, or re-routing of planned courses to circumvent resistant or tenanted occupation, could significantly add to the aqueduct's eventual length, and thus to its cost.

[20] Regulations and restrictions necessary to the aqueduct's long-term integrity and maintenance were not always readily accepted or easily enforced at a local level, particularly when ager publicus was understood to be common property, to be used for whatever purpose seemed fit to its user.

[21] In the aftermath of the Second Punic War, the censors exploited a legal process known as vindicatio, a repossession of private or tenanted land by the state, "restoring" it to a presumed ancient status as "public and sacred, and open to the people".

In 179 BC the censors used the same legal device to help justify public contracts for several important building projects, including Rome's first stone-built bridge over the Tiber and a new aqueduct to supplement the city's existing – but, by now, inadequate – supply.

In some parts of the Roman world, particularly in relatively isolated communities with localised water systems and limited availability of other, more costly materials, wooden pipes were commonly used; Pliny recommends water-pipes of pine and alder as particularly durable, when kept wet and buried.

Where sharp gradients were unavoidable in permanent conduits, the channel could be stepped downwards, widened or discharged into a receiving tank to disperse the flow of water and reduce its abrasive force.

A horizontal section of high-pressure siphon tubing in the Aqueduct of the Gier was ramped up on bridgework to clear a navigable river, using nine lead pipes in parallel, cased in concrete.

At Romano-Gallic Arles, a minor branch of the main aqueduct supplied a local suburb via a lead siphon whose "belly" was laid across a riverbed, eliminating any need for supporting bridgework.

On the standard, buried conduits, inspection and access points were provided at regular intervals, so that suspected blockages or leaks could be investigated with minimal disruption of the supply.

[41] Working patrols would have cleared algal fouling, repaired accidental breaches or accessible shoddy workmanship, cleared the conduits of gravel and other loose debris, and removed accretions of calcium carbonate (also known as travertine) in systems fed by hard water sources; modern research has found that quite apart from the narrowing of apertures, even slight roughening of the aqueduct's ideally smooth-mortared interior surface by travertine deposits could significantly reduce the water's velocity, and thus its rate of flow, by up to 1/4.

In Rome, where a hard-water supply was the norm, mains pipework was shallowly buried beneath road kerbs, for ease of access; the accumulation of calcium carbonate in these pipes would have necessitated their frequent replacement.

[43] Full closure of any aqueduct for servicing would have been a rare event, kept as brief as possible, with repair shut-downs preferably made when water demand was lowest, during the winter months.

[46][47][48] Aqueduct mains could be directly tapped, but they more usually fed into public distribution terminals, known as castellum aquae ("water castles"), which acted as settling tanks and cisterns and supplied various branches and spurs, via lead or ceramic pipes.

[51] Frontinus thought dishonest private users and corrupt state employees were responsible for most of the losses and outright thefts of water in Rome, and the worst damage to the aqueducts.

His De aquaeductu can be read as a useful technical manual, a display of persuasive literary skills, and a warning to users and his own staff that if they stole water, they would be found out, because he had all the relevant, expert calculations to hand.

Rome had no permanent central body to manage the aqueducts until Augustus created the office of water commissioner (curator aquarum); this was a high-status, high-profile Imperial appointment.

[57] Particular sections of Campania's very long, complex, costly and politically sensitive Aqua Augusta, constructed in the early days of the Augustan principate were supervised by wealthy, influential, local curatores.

The curator aquarum had magisterial powers in relation to the water supply, assisted by a team of architects, public servants, notaries and scribes, and heralds; when working outside the city, he was further entitled to two lictors to enforce his authority.

In the countryside, permissions to draw aqueduct water for irrigation were particularly hard to get; the exercise and abuse of such rights were subject to various known legal disputes and judgements, and at least one political campaign; in 184 BC Cato tried to block all unlawful rural outlets, especially those owned by the landed elite.

At Dolaucothi, the miners used holding reservoirs, as well as hushing tanks and sluice gates to control flow, and drop chutes were used for the diversion of water supplies.

A number of other sites fed by several aqueducts have not yet been thoroughly explored or excavated, such as those at Longovicium near Lanchester, south of Hadrian's wall, in which the water supplies may have been used to power trip-hammers for forging iron.

At Barbegal in Roman Gaul, a reservoir fed an aqueduct that drove a cascaded series of 15 or 16 overshot water mills, grinding flour for the Arles region.

They made a new bed for the river, so it is said, of lead, and channels at one and the other end of the city for its entrances and exits, both for watering horses and for other services convenient to the people, and anyone entering it at any other spot would be drowned.

[79]During the Renaissance, the standing remains of the city's massive masonry aqueducts inspired architects, engineers and their patrons; Pope Nicholas V renovated the main channels of the Roman Aqua Virgo in 1453.