An artificial channel for conveying water, usually by gravitation. The term (from the Latin aqua, water; and ducere, to lead) is most commonly understood to mean a bridge of stone, iron, or wood, for allowing the passage of water across a valley. But a pipe, open channel, or a tunnel through a mountain is equally an aqueduct, if its purpose is to convey water from one place to another. All great aqueducts have been constructed for the purpose of conducting water from some more or less distant source to large towns or cities. The term is also applied to a bridge carrying a canal for the purposes of navigation.
The bridge portions of an ancient Roman aqueduct consist most frequently of one row of arches, but sometimes, as shown in the illustrations, of two, and occasionally, when the height is great, even of three tiers. Some of these were built of hewn stone and others of brick, but in nearly every case they were very substantially constructed. The water channel is one or two of the larger ones is about 5½ feet high and 4 feet wide. This was, of course, formed in the upper part of the structure, above the arches, and was covered on top, bottom, and sides with a lining composed of lime, sand, and pulverized brick, which in time became as hard as stone. The gradient of these ancient aqueducts was generally about 1 in 200, a much greater slope than is given to modern works of a similar kind. Reservoirs (castella) were built at regular intervals along the aqueducts to enable repairs to be made, and to supply water, where necessary, to the inhabitants of the outlying districts.
At first sight it may seem surprising that the Romans built expensive aqueducts, but they were unable to make cast-iron pipes, or to devise other means, for carrying water underground for great distances. The aqueducts supplying Roman in Imperial times brought more than 200 million gallons of water a day into the city.
The first Roman aqueduct was built into 312 BC by the Censor Appius Claudius and was called the Aqua Appia after him. This ran through tunnels because the Romans had noy yet discovered the use of the arch; also, Rome still had powerful enemies in Italy, and an aqueduct above ground was more liable to be attacked and destroyed.
Later, however, the Romans learned the use of the arch from the Etruscans and they also removed the danger of attack by subduing all their enemies. So in 144 BC the Aqua Marcia was built, carrying the water to Rome across ravines and rivers on arches.
The finest of the Roman aqueducts is the Aqua Claudia, built in AD 38 by the Emperors Caligula and Claudius; it brought water to Rome from a place 45 miles away. Large portions of it are still standing in the countryside around Rome, and some of the arches are over 100 feet high. The three ancient aqueducts which still bring water to modern-day Rome are the Aqua Virgo, Aqua Trajana, and the Aqua Marcia. The Aqua Virgo, now called Acqua Vergine, was restored by Pope Nicholas V in 1453. Its name is said to have originated from a young girl having pointed out the spring at its source to some soldiers. The aqueduct was made by Agrippa, and finished about the year 27 BC. It mainly consists of a subterranean channel 14 miles long, and supplies daily about 13 million cubic feet of water. The Aqua Trajana was restored, in 1611, by order of Paul V, hence its modern name Acquala Paola. It stretches from Rome to the lake of Bracciano, a distance of 31 miles. The Aqua Marcia was constructed by the praetor Q. Marcius Rex in 146 BC and is 56 miles long. It was restored in 1869 and brings water from the Sabine Mountains. The impressive arches that stretch across the Campagna for some 6 miles on the road to Frascati are part of this aqueduct. Besides these three repaired ancient aqueducts, a fourth of comparatively recent date supplies modern Rome. This is the Acqua Felice, completed by Sixtus V in 1585, and largely built of material taken from the arches – about 10 miles in length – of the ancient Aqua Claudia. The length of the Acqua Felice is some 13 miles, and two-thirds of it is subterranean.
Provincial Roman aqueducts
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