low level it could not affect the other waters, but the Anio Novtis being of a lofty level and unfailing in its stream, was occasionally used, when the other aqueducts were falling off in their supply, to make good the deficiency, and hence all were more or less contaminated — even the Marcia, which was the delight of the Romans for its limpidity and coolness. The Emperor Nerva undertook to correct this evil. He began by classing the aque- ducts according to the goodness of their waters. The Marcia was reserved solely for drinking — others according to their qualities, to other uses, and the Anio Vetus, as the most impure, was reserved for the irrigation of gardens and the cleaning of the streets and sewers. He then caused the water from the Anio Novus to be drawn from the lake itself, instead of the river ; and either because the stream supplying this lake ran over a rocky bed, or that from the depth of the lake, the water was purified by depositing an earthy matter, it issued thence cool and bright, so as to equal in appearance and taste the Marcia, which it greatly surpassed in quantity. Nerva caused numerous wells to be constructed in the courses of the other aqueducts, in which the waters deposited their sediment. He also framed regulations for the gene- ral distribution of the water, by means whereof a more vigilant supervision was ex- ercised, and a considerable increase was effected in the quantity indicated by the registers. The whole supply furnished by the nine aqueducts is thus stated by Frontinus, the measurement being made at the head of each aqueduct, except of the Julia and Virgo, which are calculated from their registers of delivery : Anio Vetus, 4,398 quinariae. Aqua Appia, 1,825 quinariae. Aqua Marcia, 4,690 « « Tepula, 445 " " Virgo, 2,504 « Anio Novus, 4,738 -« " Julia, 1,368 « « Claudia, 4,607 " 7008 17,567 17,567 quinariae 24,575 The quantity of the Alsietina is not given, but it was computed to deliver about 400 quinariae— making altogether, 25,000 quinariae.* * The quinaria is equivalent to about 2000 cubic feet, of about 7 gallons each. 20 PRELIMINARY ESSAY. But of this immense abundance, not three-fifths, according to the public registers, were lawfully delivered, the rest being surreptitiously abstracted by individuals. The whole daily supply shown by these registers, was 14,018 quinarise, equal to about 28,000,000 cubic feet, or one hundred and ninety-six million gallons ! Notwithstanding this pro- digious abundance of water supplied by the aqueducts, which Strabo compares to rivers flowing along the streets and through the sewers, the use of well and spring water was not abandoned. The population of Rome* at the period when Frontinus wrote, between 70 and 80 years after the Christian Era, may be taken at between 1,000,000 and 1,200,000. Assuming it at one million, the daily supply of water from the aqueducts to each inhabi- tant, was 196 gallons ! The supply of London, now containing more than two millions of inhabitants, is computed at 37,000,000 gallons, or about one-fifth of that of ancient Rome. The city of Paris is still more deficient in this resource. The distribution of the water along its course, as well as throughout the city, was re- gulated with scrupulous care. Besides the piscina limosa, or purify ing reservoir usually placed at the mouth of each aqueduct, there were frequent castella, or wells along the line, which both aided in the process of purification, and permitted water to be drawn occa- sionally along the route, for the irrigation of fields and gardens, and the supply of baths. The main castellum was that in which the aqueduct terminated, and whence the water was distributed through the city. These were vast, solid, and stately architectural struc- tures. The mass of ruins now called "The Trophies of Marius," from some very vague tradition, are undoubtedly the remains of a vast castellum, in which, according to the conjecture of Burgess, the Aqua Julia, and the Claudia, were received. The Pis- cina MirabileJ near Cumae, is a "stupendous structure of 200 feet in length, by 130 in breadth, whose vaulted roof rests 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