Roman Aqueducts

Ancient Rome had eleven major aqueducts, built between 312 B.C. (Aqua Appia) and 226 A.D. (Aqua Alexandria); the longest (Anio Novus) was 59 miles long. It has been calculated that in imperial times, when the city's population was well over a million, the distribution system was able to provide over one cubic meter of water per day for each inhabitant: more than we use nowadays. For most of their length the early aqueducts were simply channels bored through the rock, from the water intake in the hills almost to the distribution cistern in Rome. The depth of the channel below ground varied so as to maintain a constant, very shallow gradient (less than 1/200) throughout the length of the aqueduct; vertical shafts were bored at intervals to provide ventilation and access. Only in the final stretches was the conduit raised on arches, to give a sufficient head for distribution of the water within the city. In order to keep the gradient constant, the aqueducts took a roundabout route, following the contours of the land and heading along spurs which led towards Rome. The most dramatic parts of a Roman aqueduct wereÐ'--and still areÐ'--the bridges (also known as arcades) that carried the water over low spots in the terrain. Perhaps the best-known of these is the Pont du Gard, a part of the aqueduct that served the town in NÐ"®mes in Gaul (today's France). The bridge stands on three tiers of arches and has a length of 274 m (900 ft). Built without the use of mortar, it stands 49 m (160 ft) above the BornÐ"Ёgre Ravine. Another famous Roman aqueduct is the one in Segovia, Spain; it still carries water, although it did need restoration in the 15th century. s time went on, Roman engineers became more daring in the construction of high arches to support the conduits across valleys and plains and some of the later aqueducts were as much as 27 meters (about 100 feet) above ground level in places. Closed pipes were occasionally used to cross