This Aqueduct was made by Marcus Vipsanius Agrippa to supply water to his Thermæ, on the south side of the Pantheon, which was the hall of entrance to them. Frontinus writes:— “The same (M. Agrippa) when he had been consul for the third time, and when C. Sentius and Quintus Lucretius were consuls, that is, thirteen years after he had brought down the Julia, he brought the ‘VIRGO’ also, the water of which was collected in the Lucullan fields[93]. “The Virgo begins on the Via Collatia, at the eighth milestone, in some marshy places: a cemented wall [_signino[94] circumjecto_] being placed round it, to retain the bubbling waters; the source was increased by many other additional supplies. It comes for a length of 14 miles and 105 paces. Out of this,—by a subterranean stream 12 miles, 865 paces; above ground for 1 mile, 240 paces, of which it runs on a substructure in several places for a distance altogether of 540 paces; on arched work 700 paces. The channels of the additional supplies of the subterranean stream make 1 mile, 405 paces[95].” The Virgo has no reservoir, i.e. Piscina ... “The arches of the Virgo have their commencement beneath the Lucilian (or Lucullan?) gardens. They end in the Campus Martius, along the front of the Septa[96].” The Virgo was the seventh in height as to level (c. 18). The road now called Via Collatia, or Collatina, where the Aqua Virgo has its origin, is between the present roads to Tivoli and Palestrina; it turns off to the left or north of the highway now called Via Prænestina, just beyond the ruins called Torre de’ Scavi or de’ Schiavi, about three miles from the city. But this is an alteration; the old road from Rome to this point in a foss-way may be traced _behind_ the tower in the meadows, with the subterranean aqueduct running under and in the southern bank of it, as traced by the respirators or ventilating shafts. There are remains of very ancient tombs at intervals all along the line of this old road, which goes straight towards a postern-gate midway between the Porta Maggiore and the Porta di S. Lorenzo. This must be the Via Collatia of Frontinus. Close to this road, at eight miles from Rome, near the ruins of Collatia, there are several springs in marshy ground, from which the water is collected in a series of reservoirs, just below the level of the ground, the vaults over them being sometimes above ground; from these small reservoirs separate short conduits run to the same point, the great central _castellum aquæ_, part of which is a cave in a rock, with a larger semicircular basin built out in front of it, over which passes the cross-road from the Via Collatia to Salone. The line of the _specus_ can be distinctly traced from this reservoir near its source to the city by the respirators over the wells. The smaller _castella_, or cisterns, at the sources are also still in use.