their aqueducts in the ground, in order that they might not easily be cut by the enemy, since frequent wars were still waged with the Italians. But now, wherever a conduit has succumbed to old age, it is the practice to carry it in certain parts on substructures or on arches, in order to save length, abandoning the subterranean loops in the valleys.[1] The sixth rank in height is held by Old Anio, which would likewise be capable of supplying even the higher portions of the City, if it were raised up on substructures or arches, wherever the nature of the valleys and low places demands. Its elevation is followed by that of Virgo, then by that of Appia. These, since they were brought from points near the City, could not rise to such high elevations. Lowest of all is Alsietina, which supplies the ward across the Tiber and the very lowest districts.
Of these waters, six are received in covered catch-basins, this side the seventh milestone on the Latin Way. Here, taking fresh breath, so to speak, after the run, they deposit their sediment. Their volume also is determined by gauges set up at the same point.[2] Three of these, Julia, Marcia, and Tepula, are carried by the same arches from the catch-basins onward. Tepula, which, as we have above explained,[3] was tapped and added to the conduit of Julia, now leaves the basin of this same Julia, receives its own quota of water, and runs in its own conduit, under its own name. The topmost of these three is Julia; next below is Tepula; then Marcia.[4] These flowing [under ground] reach the level of the Viminal Hill, and in fact even of the Viminal Gate. There they again emerge. Yet a part of Julia is
