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 general by means whereof a more vigilant supervision was exdistribution of the water,

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 " Anio Novus, 4,738 -

Virgo, 2,504 " Julia, 1,368 " 7008 Claudia, 4,607 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