The aqueduct at Segovia has an arched masonry structure nearly half a mile long, hav ing 109 arches which reach a height of slightly over 100 feet. The aqueduct at Tarragona, Spain, is 876 feet long and 83 feet high; that at Metz, built in the 4th century A.D., now partly in ruins, was carried across the river Moselle by a masonry structure 60 feet high; that at Antioch, 'Syria, of rather unusual design, is 700 feet long and 200 feet high; that at Moris is about 500 feet long and 80 feet high, built in three tiers of arches, the uppermost of which is of brick. The Roman aqueduct at Carthage was about 60 miles long, a part of it carried by an arched masonry structure about 50 feet high. Many other notable aqueducts were built in early Roman times in Europe, Asia Minor and Africa.
With the decline of the Roman empire the building of great aqueducts almost ceased dur ing the Middle Ages, though there are a few notable examples. That at Spoleto, Italy (800 900 A.D.), seems to have been the first instance where the Gothic arch was introduced into aqueduct work. With a height of 300 feet and its 10 arches of 66 feet span, it was of espe cially light and graceful design. Among sev eral mediaeval aqueducts at Constantinople, that of Justinian ("Muallak KemerD) is re markable for the beauty and excellence of its design and construction. It is 720 feet long and 108 feet high, having two tiers of pointed arches, the lower having spans of 55 feet and the upper ones of 40 feet.
The Greeks and Romans had little choice in the materials or methods of aqueduct build ing. Large pipes, of any material, were not available, though where pressure was to be re sisted the earlier builders sometimes used as a substitute large blocks of stone pierced with a hole of the required size for the conduit, the faces of the blocks being dressed to fit to gether and to make joints as nearly water tight as possible. The Romans built their water conduits, both in tunnels and over via ducts, of masonry lined internally with Roman cement. The driving of long tunnels, often at considerable depths below the surface, must have been a slow and costly process with the tools and methods then known. The difficulties of following correct alignments and gradients underground, with the knowledge and instru ments then available, were very great, as evi denced by the tortuous course of many of these tunnels. For the elevated structures stone masonry was the only adequate construc tion then available. The extensive use of hy
draulic concrete had not been developed, though occasionally employed, but Roman cement was generally used for water-proofing. Their masonry was generally built up of large blocks of granite or other hard and durable rock, with fairly well-dressed joints, laid dry; that is, with out mortar. Their foundation work seems to have been of a high order, for foundation fail ures in these great structures were very rare. Brick was used to some extent, especially in their later constructions, and there are ex amples of brick-faced masonry backed by concrete.
Modern The resumption of aqueduct building on a large scale dates back less than 200 years, and most of the aqueducts of any considerable magnitude are of quite recent construction. A few of the more notable on the eastern continents may be men tioned.
Marseilles has a (now navigable) canal, constructed 1837-48, 97 miles long, connecting the river Durance with the Mediterranean, and the city's water supply is carried from this canal over the river Arc by the magnificent masonry aqueduct of Roquefavour.
The Thirlmere Aqueduct supplies Manches ter with about 50,000,000 gallons of water per day, bringing it from lakes 96 miles from the city. Of this length, 14 miles are in tunnel, 37 miles are "cut and cover° work, with a water channel 7x7 feet, and 45 miles are of cast-iron pipes, the design being for five pipes of 40 inches internal diameter adjacent to each other, only three of which have yet been laid. (The term "cut and cover° work may be briefly defined as a conduit of masonry or other material, constructed in an excavated trench wide enough to receive it and of such depth that when completed and the excavated material filled back, the conduit will be entirely covered and thus become, in effect, a tunnel). The cost of this aqueduct in its present condi tion has been in the neighborhood of $20,000, 000.
Liverpool is supplied with water from the river Vyrnwy in northern Wales, delivered through an aqueduct 68 miles long, consisting, for the most part, of two lines of cast-iron pipe from 39 to 42 inches in diameter, provision be ing made for a third pipe when it becomes necessary. The fall from the Vyrnwy to Liv erpool is so great (550 feet) that it was neces sary to relieve the pressure in the pipes by in terposing equalizing reservoirs at a number of different points. Birmingham is supplied with 75,000,000 gallons daily by an aqueduct 74 miles long.