The piscinas or reservoirs, to which reference has been made, were placed at a certain distance from the city, and there the waters deposited their sediment, and there also the quantity of the supply was determined by a register ; six of the aqueducts were thus emptied into piscinas; three of these, the Julia, Marcia, and Tepula were conducted from the purifying reservoirs to the city, over the same aqueduct, as has already been noticed, one above the other. The Anio Novus, and the Claudia also flowed in separate channels over the same arches. The Anio Vetus had a separate series of arches. Neither the Virgo, Appia, nor Alsietina were supplied with piscinas.

* Stuart's Die. of t Stuart's Archi., art. Aqueducts. Archi., art. Aqueducts.

PRELIMINARY ESSAY. ly

At this period it would appear that after a heavy fall of rain, the greater part of the water flowing into the city by all the aqueducts, was discolored by the mixture of earthy matters, even some that were pure and limpid at their sources. This impurity was particularly observable of the two Anios that were supplied from a river, which although,

flowing from a lake of great transparency, passed through a rich soil, which in seasons of rain rendered the waters turbid. Indeed, the Anio Vetus was rarely free from discoloration, but as it flowed on a 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.