upon forty-eight immense pillars, disposed in rows, so as to form five aisles within the edifice, and sixty arches." The castellaMvere of three kinds, public, private, and domestic.}: The public castella which received the water of the aqueduct, were such as have already been described, and from them distribution was made : 1st., to the Praetorian camps ; 2d., to the fountains, and pools in the city ; 3d., the Munera, under which head are comprised the places where the public shows and spectacles were given, such as the circus, amphitheatre, naumachiae, &c.; 4th., public works or establishments, such as the * See Gibbon, Dec. and Fall, vol. iv., p. 105, et sequ, for a computation of the population of Rome, t Antiquities of Rome, vol. i., p. 199. j Anthon's Die., art. Aqueducts. PRELIMINARY ESSAY. 21 baths, and the trades of fullers, dyers, tanners, &c., which, though conducted by private persons, were deemed public, inasmuch as they were necessary to the general con- venience and comfort; 5th. and 6th., under the terms of nomine Ccesaris, (in the name of Caesar,) and beneficia Principis, (benevolence of the Prince,) were certain irregular distributions, or extraordinary grants, to places or individuals. Castella Prlvata. When a number of individuals, living in the same neighborhood, had obtained a grant of water, they clubbed together and built a castellum^ into which the whole quantity allotted to them collectively, was transmitted from the castellum publicum. These were termed privata, though they belonged to the public, and were under the care of the curatores aquarum. Their object was to facilitate the distribution of the proper quantity to each person, and to avoid puncturing the main pipe in too many places ; for when a supply of water from the aqueducts was first granted for private uses, each person obtained his quantum by inserting a branch pipe, as we do, into the main, which was pro- bably the custom in the age of Vitruvius, as he makes no mention of private reservoirs. In- deed, in earlier times, all the water brought to Rome by the aqueducts, was applied to public purposes exclusively, it being forbidden to the citizens to divert any portion of it to their own use, except such as escaped by flaws in the ducts or pipes, which was termed aqua ca- duca. But as even this permission opened a door for great abuses, from the fraudulent con- duct of the aquarii, who damaged the ducts for the purpose of selling the aqua caduca, a remedy was sought by the institution of castella privata, and the public were hence- forward forbidden to collect the aqua caduca, unless permission was given by special favor (beneficium) of the emperor. The right of water (jus aquce impetratce) did not follow the heir or purchaser of the property, but was renewed by grant upon every change in the possession. Castella Domestica, leaden cisterns, which each person had at his own house to re- ceive the water laid on from the castellum privatum. These were, of course, private property. The number of public and private castella in Rome at the time of Nerva, was 247. All the water which entered the castellum was measured, at its ingress and egress, by the size of the tube through which it passed. The former was called modulus accep- toriuSj the latter erogatorius. To distribute the water was termed erogare ; the distribu- tion, erogatio ; the size of the tube, fistularum or modulorum capacitus, or lumen. The smaller pipes which led from the main to the houses of private persons, were called punctoe ; those inserted by fraud into the duct itself, or into the main after it had left the castellum, fistula, illicitce. The erogatio was regulated by a tube called calix, of the diameter required, attached 6 22 PRELIMINARY ESSAY. to the extremity of each pipe where it entered the castellum ; it was probably of lead in the time of Vitruvius, such only being mentioned by him ; but was made of bronze (aneus) when Frontinus wrote, in order to check the roguery of the aquarii, who were able to increase or diminish the flow of water from the reservoir by compressing or extending the lead. Pipes which did not require any calix were term ed solutce* The fact referred to in the last paragraph, of the increase and diminution of the quantity of water flowing through a tube, by altering its shape, is of sufficient interest to authorise some further notice of it. It must be stated in the first place, that more water will flow through a short tube than through a simple orifice of the same diameter. It may be thus ascertained : bore a hole of an inch diameter in a bucket, plug it up, and, having