<P> Hundreds of similar 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 is 92.5 km (57.5 mi) in length . It was built in the 2nd century to supply Carthage (in modern Tunisia). Surviving aqueduct bridges include the Pont du Gard in France and the Aqueduct of Segovia in Spain . The longest single conduit, at over 240 km, is associated with the Valens Aqueduct 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". Rivalling this in terms of length and possibly equaling or exceeding it in cost and complexity, is the provincial Aqua Augusta that supplied an entire region, which contained at least eight cities, including the major ports at Naples and Misenum; sea voyages by traders and the Roman navy required copious supplies of fresh water . </P> <P> Whether state - funded or privately built, aqueducts were protected and regulated by law . Any proposed aqueduct had to be submitted to the scrutiny of civil authorities . Permission (from the senate or local authorities) was granted only if the proposal respected the water rights of other citizens; on the whole, Roman communities took care to allocate shared water resources according to need . The land on which a state - funded aqueduct was built might be state land (ager publicus) or privately owned, but in either case was subject to restrictions on usage and encroachment that might damage the fabric of the aqueduct . To this end, state funded aqueducts reserved a wide corridor of land, up to 15 feet each side of the aqueduct's outer fabric . Ploughing, planting and building were prohibited within this boundary . Such regulation was necessary to the aqueduct's long - term integrity and maintenance but was not always readily accepted or easily enforced at a local level, particularly when ager publicus was understood to be common property . Some privately built or smaller municipal aqueducts may have required less stringent and formal arrangements . </P> <P> Springs were by far the most common sources for aqueduct water; for example, most of Rome's supply came from various springs in the Anio valley and its uplands . Spring - water was fed into a stone or concrete springhouse, then entered the aqueduct conduit . Scattered springs would require several branch conduits feeding into a main channel . Some systems drew water from open, purpose - built, dammed reservoirs, such as the two (still in use) that supplied the aqueduct at the provincial city of Emerita Augusta . </P> <P> The territory over which the aqueduct ran had to be carefully surveyed to ensure the water would flow at an acceptable gradient for the entire distance . Roman engineers used various surveying tools to plot the course of aqueducts across the landscape . They checked horizontal levels with a chorobates, a flatbedded wooden frame fitted with a water level . They plotted courses and angles could be plotted and checked using a groma, a relatively simple apparatus that was probably displaced by the more sophisticated dioptra, precursor of the modern theodolite . In Book 8 of his De Architectura, Vitruvius describes the need to ensure a constant supply, methods of prospecting, and tests for potable water . </P>

Where did the water for the roman aqueducts come from
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