Page:Encyclopædia Britannica, Ninth Edition, v. 2.djvu/235

Rh 219 A QUEDUCT, a conduit or channel for the conveyance XJL of water (Lat. aquasductus), but commonly a structure of masonry erected to conduct water across a valley at a high level, though structures of this kind would be more pro perly termed aqueduct bridges. This distinction it is necessary to bear in mind, more particularly when dealing with the undertakings of this class carried out by the Greeks and Romans respectively, because, from the fact of the former having apparently seldom if ever constructed aqueduct bridges, it has been usual to institute a very unfavourable comparison between them and the Romans, who, with imperial disdain of obstacles, furnished the cities of their immense empire with a series of constructions of this kind for the supply of water, which still in their ruins excite our astonishment. True to the difference in national genius the Greeks, following the analogy of nature, in which in their own country they saw the water collected in the hills passing for miles along subterranean courses, and issuing in cool fountains at the coast, adapted their system of conduits to the physical formation of a district, cutting tunnels and canals, rather than bridging over valleys, and as a consequence no conspicuous monument of their system now remains. But even if what they did was so little as to justify Strabo (v. p. 235) in charging them with neglect in this matter as compared with the carefulness of the Romans, it is still clear from the records that they accomplished much, and that in this, as in other respects, they were the instructors of the Romans. It is here to be premised that the term aqueduct applies only to the conveyance of such water as was used for drinking or other useful purposes, and not to the draining of marshes, though in both cases the works may often have been of the same kind. The insufficiency of water, supplied by natural springs and cisterns hewn in the rock, which in an early age had satisfied the small communities of Greece, had become a pressing public question by the time of the Tyrants, of whom Polycrates of Samus and Pisistratus of Athens distinguished their rule by extensive works to meet the exigencies of their states. For this purpose the former obtained the services of Eupalinus, an engineer celebrated for the skill with which he had carried out the works for the water supply of Megara, under the direction of the Tyrant Theagenes (circa G25 B.C.) At Samus the difficulty lay in a hill which rose between the town and the water source. Through this hill Eupalinus cut a tunnel 8 feet broad, 8 feet high, and 4200 feet long, building within the tunnel a channel 3 feet broad and 1 1 ells deep. The water, flowing by an accurately reckoned declivity, and all along open to the fresh air, was received at the lower end by a conduit of masonry, and so led into the town, where it supplied fountains, pipes, baths, cloaca?, &c., and ultimately passed into the harbour. In Athens, under the rule of Pisistratus (B.C. 5GO), a similarly extensive, if less difficult, series of works was completed to bring water from the hills Hymcttus, Pentelicus, and Parnes. From Hymet- tus were two conduits passing under the bed of the Ilissus, and most part of the course cut in the rock. Peutelicus, richer in water, supplied another condmt, which can still be traced from the modern village of Chalandri by the air shafts built several feet above the ground, and at a dis tance apart of 40-50 metres ; the diameter of these shafts is 4-5 feet, and the number of them still preserved is about sixty. Tributary channels conveyed into the main stream the waters of the district through which it passed. Outside Athens, those two conduits met in a large reser voir, from which the water was distributed by a ramification of underground channels throughout the city. These latter channels vary in form, being partly round, partly square, and generally walled with stone ; the chief one, that under the bazaar, is sufficiently high and broad to allow two men to pass in it. Sometimes pipes of baked clay were laid within them. The conduit from Mount Parnes appears to have been reconstructed in later times. Some of these aqueducts continue to supply Athens to this day, and are described as marvels of enterprise and skill (E. Curtius, iiber die Wasserlxtuten der Hellenen. in the Archdol. Zeit. 1847, p. 19). In Sicily, the works by which Empedocles, it is said, brought the water into the town of Selinus, are no longer visible ; but it is probable that, like those of Syracuse, they consisted chiefly of tunnels and pipes laid under ground. The system of conduits in Syracuse which Thucydides says (vi. 100) the Athenians partly destroyed on the Sicilian expedition, still supplies the town with an abundance of drinkable water; and at one point, where the tunnel passes under the sea to the island of Ortygia, presents what has long been regarded as a remarkable achievement for early times. An example of what appears to have been the earliest form of aqueduct in Greece has been discovered in the island of Cos (Ross, Inselreise, iii. p. 131), beside the fountain Burinna on Mount Oromedou. It consists of a bell-shaped chamber, built underground in the hill side, to receive the water of the spring and keep it cool; a shaft rising from the top of the chamber supplied fresh air. From this reservoir the water was led by a subterranean channel, 35 metres long and 2 metres high. Of the constructions for the conveyance of water in Italy in early times, there is an example at Tusculum, consist ing of an oblong basin, divided into several chambers, which received the water of a spring, and then distributed it by pipes (tuli, fistuloe) or canals. The basin is built of blocks of stone, which, along the sides, overlap each other, till they meet and form a roof a principle of building which was afterwards supplanted by vaulting, and which occurs also in the earliest Greek masonry. The pipes were either of lead or baked clay. When the course lay in soil, gullies were cut and conduits of masonry built within them. When rocky ground intervened, tunnels were pierced, and in both cases shafts (spiramen. lumen} were made at intervals of about 240 feet, to admit light and fresh air. The inside of the walls of these channels received a coating impervious to water, composed of chalk and crushed fragments of tile. Where the course was interrupted by an inequality in the ground, a vertical pipe (venter) was placed reaching to the surface or above it. The water rushing up this pipe was freshened by contact with the air, and again fell back to the new course which it had to take. Works of this kind, undertaken for the public convenience, were paid for out of the public purse, a tax being levied for the use of the water. If, to obtain a proper incline, the water-course had to be carried above ground, the simple plan was to support it on a stone wall, and in this case the conduit itself was also built of blocks of stone, coated with a stucco impervious to water. But since a solid wall across a valley would have cut off the usual traffic, it was found necessary to break up the wall, by means of arches, into a series of pillars, and with this commenced the system of aqueduct bridges, which have proved to be the most striking monuments of the Roman empire. As perhaps the best known instance of this double purpose, of an archway under which traffic might pass, and over which water might be conveyed, there is the Porta Maggiore at Rome (Plate III.) The waters