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Aqua Claudia, though of such different heights at Rome, have their sources at the same elevation.
At convenient points on the course of the aqueduct, and especially near the middle and end, there was generally a reservoir (piscina, piscina limosa} in which the water might deposit any sediment that it contained. The construction of these reservoirs will be understood from the following woodcut, which represents a restored section of one which still exists.
The water flowed from the aqueduct a into the first upper chamber, thence down and up again through the openings b, c, e, into the second upper chamber, out of which it passed into the continuation of the aqueduct /, having deposited its sediment in the two lower chambers, which could be cleaned out by the door d. The piscina was not always vaulted: Hirt, from whose work the above cut is taken, gives also an engraving of an open piscina. These reservoirs were not always used: for example, the Aqua Virgo and the Alsietina were without them. They were especially necessary when the water was conveyed through pipes. They were also used as reservoirs for the supply of the neighbouring country, chiefly for the purposes of irrigation.
The details, which we have now been noticing, are minutely described by Frontinus, and by Vitruvius* (viii. c. 7. s. 6), and briefly by Pliny (H. N. xxxi. 6. s. 31).
(3.) The Termination of the Aqueduct, and tlie Arrangements for the Distribution of its Water. — The water thus conducted to the city was received, when it reached the walls, in a vast reservoir called castellum, which formed the head of wafer and also served the purpose of a meter. The more ancient name in use, when the aqueducts were first constructed, was dividiculum. (Fest. s. v.) From this principal castellum the water flowed into other castelia, whence it was distributed for public and private use. The term castellum is sometimes also applied to the intermediate reservoirs already mentioned.
The chief castellum was, externally, a highly decorated building ; for example, that of Hadrian, at Athens, was adorned with Ionic pillars, and that at Evora, in Portugal, had the form of a circular temple. Internally, there was generally one vast chamber, with a vaulted roof supported by massive pillars, into which the water flowed from
*• The particular attention which Vitruvius pays to the conveyance of water through .pipes, warrants the supposition that in his time, when some of the most important of the aqueducts were not :yet erected, that method was very largely employed.
the aqueduct, and from which it was conducted through pipes of fixed dimensions, into three smaller reservoirs, which were, however, so arranged, that the middle one was only supplied from the overflow of the other two. Of these three reservoirs, the two outer supplied respectively the public baths and the private houses, and the middle one the public ponds and fountains (lacus et salientes) : so that, in case of a deficient supply for useful purposes, none would be wasted on the fountains ; the arrangement also enabled a proper account to be kept of the quantity supplied for private use, for the protection of the revenue derived from this source. (Vitruv. viii. 7. s. 6. §§ 1, 2.)
The minor casiella, which received the water from this chief head, were distributed over the city, in such a manner that the Aqua Appia supplied seven regiones by means of twenty castelia; the Anio Vetus, ten regiones through thirty-five castelia j the Marcia, ten regiones through fifty-one castelia ; the Tepula, four regiones through fourteen castelia ; the Julia, seven regiones through seventeen castelia; the Virgo, three regiones through eighteen castelia ; the Claudia and the Anio Vetus, ninety-two castelia. (Frontin. 79—86.) For an account of the parts of the city supplied by the different aqueducts, see Becker, Handb. d. Rom. Alterth. vol. i. pp. 707, 708.
The subjoined plan and elevation represent a ruin still remaining at Rome, commonly called the " Trophies of Harms," which is generally considered to have been the castellum of an aqueduct.
V^Ms * -^-*~f^-'~——— H '—————"——•—' ** ill "
It is now much dilapidated, but was tolerably entire about the middle of the 16th century, as may be seen by the drawing published by Gamucci (Antichitadi Roma, iii. p. 100), from which this restoration is made. The trophies, then remain-ing^ in their places, from which the monument derives its modern appellation, are now placed on the Capitol. The ground plan is given from an excavation made some years since by the students of the French Academy ; it explains part of the internal construction, and shows the arrangement adopted for disposing of the superfluous water of an aqueduct. The general stream of water is first divided by the round projecting buttress into two courses, which subdivide themselves into five minor streams, and finally fall into a reservoir.
The castelia were divided into two classes, the publica and privata.