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Sity that- led to the invention of aqueducts, in order to bring pure water from a considerable distance, from the hills, in fact, which surround the Campagna. The date of the first aqueduct is assigned by Frontinus to the year A. u. c. 441, or b.c. 313 (De Aquaed. Urb. Rom. 4, p. 14, ed. Adler) ; and the number of aqueducts was gradually increased, partly at the public expense, and partly by the munificence of individuals, till, in the time of Procopius, they amounted to fourteen ; and, even before they were all erected, they might well excite the admiration which Pliny expresses with respect to the Claudian aqueduct, in the following passage (H. N. xxxvi. 15. s.24) : —" But if any one will carefully calculate the quantity of the public supply of water, for baths, reservoirs, houses, trenches (euripi\ gardens, and suburban villas ; and, along the distance which it traverses, the arches built, the mountains perforated, the valleys levelled ; he will confess that there never was any thing more wonderful in the whole world." But why did the Romans waste so much money and labour on works, the purpose of which might have been effected much more scientifically by the simple plan of laying pipes along the ground ? Of course, it is easy to give the unthinking answer, that they were ignorant of the laws of hydrostatics, and did not know that water finds its own level! It is truly marvellous that such an absurd notion should ever have been entertained, and yet it is the common explanation of the fact of their building aqueducts instead of laying down water-pipes. If it were at all neces-cessary to prove that a nation, so far advanced in civilisation as the Romans, or indeed that any individual arrived at years of discretion, had discovered that water finds its own level, the proof might be supplied from passages in Latin authors *, from the whole arrangements for the distribution of the water of the aqueducts, and from the
a, a, The ascending pipe.
6, 6, The basin, made of blocks of travertine.
* Vitruvius not only expressly states the law (viii. 6, s. 5), but describes one form of the aqueduct in which it was practically applied (viii. 7. s. 6), as will be seen below. Pliny also, in describing the passage of water through pipes, states the law in these very distinct terms : — " Subit ultitudinem exortus sui." (//. N. xxxi. 6. s. 31.)
very existence of their numerous fountains ; as a decisive ocular demonstration, we have given above a section of one of the many fountains still existing at Pompeii. Another reason assigned for the construction of aqueducts by the Romans is their want of the materials, and the manufacturing skill, to make pipes of a sufficient size ; combined, on the other hand, with the love of magnificence and the ostentatious disregard of expense, by which the architectural works of the empire are characterised. Some weight should doubtless be assigned to these considerations, although, in fact, the Romans made use of pipes as well as aqueducts : but the great point is, that it has been too hastily assumed that the aqueduct is an unscientific mode of conveying water to a large city from distant sources ; or that it is peculiar to the ancients. London itself is chiefly supplied by an aqueduct, for such is the New River in principle, although the country through which it'flows is such as not to require arches and tunnels like those of the Roman aqueducts ; and the remark would apply to several other great cities. The whole matter is a question of the balance of advantages. On the one hand there is the expense of the aqueduct: on the other, the enormous pipes which would be required for the conveyance of an equal quantity of water, their liability to get obstructed, and to yield at the joints, the loss by friction, especially in the bends, and the unequal pressure of the water. In fact, the most recent feat of engineering science in this department is exactly a return to the Roman aqueduct, which has been preferred to any other plan for conveying water in large quantities a considerable distance, over great inequalities of ground: we refer to the aqueduct, begun in 1837 and finished in 1842, by which the water of the river Croton is conveyed a distance of forty miles, for the supply of New York, and which is thus described : —" An artificial channel, built with square stones, supported on solid masonry, is carried over valleys, through rivers, under hills, on arches and banks, or through tunnels and bridges, over these forty miles. Not a pipe, but a sort of condensed river, arched over to keep it pure and safe, is made to flow at the rate of a mile and a half an hour towards New York." A more exact description of an ancient Roman aqueduct could not easily be given. (See Illustrations of the Croton Aqueduct, by F. B. Tower, 1843.)
The detailed description of the arrangements of the aqueduct will be better understood, after an enumeration of the principal aqueducts by which water was conveyed to Rome across the Campagna.
They were fourteen in number ; and only four of them belong to the time of the republic, while five were built in the reigns of Augustus and Claudius. Our knowledge of the subject is derived almost entirely from the treatise De Aquae-ductibus Urbis Romae, by S. Julius Frontinus, who was curator aquarmn (keeper of the aqueducts; under Nerva and Trajan. It should be observed that the Aquaeductus is often called simply Aqua.
1. The Aqua Appia was begun by the censor Appius Claudius Caecus (to whom also Rome was indebted for her first great road), in b.c. 313. Its sources were near the Via Praenestina^ between the seventh and eighth milestones, and its termination was at the salinae, by the Porta Trigemina.