At about half a mile from this _osteria_, in a hollow, is a white house called Casale Bianco; and close to this is a fountain, supplied by a spring which runs into a _specus_. This water, being one of the sources of the Aqua Paola, passes through the hill at a considerable depth. At about half the distance between this and the _osteria_ is a remarkable passage for the Aquarii into the tunnel by a very steep descent, passing sideways across the _specus_ of the Aqua Paola, and going on to a much greater depth to the Aqua Alsietina[111]. This passage is 150 ft. in length from the surface of the hill, and 70 ft. in perpendicular depth, with ninety steps, of which only a few at the top are visible; the others are covered with earth. The water still runs through the upper _specus_, and is still in use, but not through the lower one[112]. From the valley beneath the sloping passage for the Aquarii, near the Osteria Nuova, Nibby[113] traced the Alsietina as a tunnel cut in the tufa rock, a part of which he saw near an oil mill. The _specus_ then followed the low ground from the tenements of S. Niccola, Porcareccina, Maglianella, and from the Villa Panfili, to the principal gate of the monastery of _S. Cosimato_ (or SS. Cosmas and Damian in the Trastevere), where it is stated by Cassio[114] that the _specus_ was found in 1720, about thirty feet underground. The Naumachia of Augustus is said to have been near this monastery. The complaints of Frontinus appear to have been listened to by the Emperor, and great changes and improvements were made in this aqueduct under his direction, in the time of Trajan; this is in fact the same as the Aqua Trajana (see X.), and the water still comes from the Lacus Sabatina, but not from the Alsietina. In going from Rome, the respirators can be followed across Monte Mario, and near the high road that passes over Ponte Molli, to the point of junction about ten miles on the road to the Cariæ [now Osteria Nuova]. Here the respirators cease; but their place is supplied by a line of old wells descending into the subterranean _specus_, which follows the line of the _old road_. This is not always the same as the new one. The other branch, which supplied the Naumachia, was the only one made in the time of Augustus. Paul V. repaired this aqueduct along the whole line, restored it to use, and put up in various places inscriptions recording this, in which he calls it the Aqua Alsietina[115]. The last of these is on his fountain at the mouth of the aqueduct, where the water still gushes out in great abundance, as it did in the sixth century, when it was observed by Procopius; this is on the Janiculum, above S. Pietro in Montorio, the highest ground in Rome. VIII., IX. THE CLAUDIA AND ANIO NOVUS (A.D. 52).