These three may all be treated as one aqueduct for the supply of Rome, partly natural and partly artificial. They all come from the Alban Hills; the first from near Rocca di Papa on very high ground, the second from about a mile above the small and very picturesque town of Marino; the third lower down the same hill. They are all mountain streams, and partake of the usual character of such streams; in dry weather the springs that supply the Almo bring so little water, that it is only sufficient to fill some ponds for cattle at the foot of the hill. The deep bed of the river, which winds about the Campagna for miles, is therefore dry for a great part of the year, but the other two streams never fail; they are united at the foot of the hill, not far from the place where the Aqua Aurelia came from. The greater part of their united waters runs into the river Anio, but a portion of it is diverted near the ruins of the ancient fortified village or _pagus_, called _Centroni_ (2315, 2316, 2317, 2318, 2319), on the road to Tusculum, (now Frascati,) about eight miles from Rome. This branch to supply Rome is first brought through an ancient tunnel of the Aqua Julia, at each end of which remains can be seen of the stone _specus_ and the flood-gates (2310, 2311, 2312, 2313). The water is then conveyed in a bank of clay for about a mile, and then in the bed of one of the many branches of the mountain stream called the river Almo, and so brought into Rome (1309, 1318), under the Porta Metronia, which is built upon a bridge over it. The stream passes under some other bridges with mills upon them, and eventually falls into the Tiber through an aperture left for it in the Pulchrum Littus, or fine tufa wall of the Kings (drawing, 1235*; plans, 368*, 1234*; views, 77, 166, 157). Another branch from it is carried from the junction or separation between the Torre Fiscale and Roma Vecchia (1937*) by the side of the cross road from the Via Appia Nova to the Via Appia Antiqua. Sometimes in the bed of the Almo, and in other parts, where the ground is low and the stream is liable to floods, an artificial canal is made for it, which may be seen in the valley of the Caffarella. This excellent plan was carried out in the most economical but effectual manner by a company in the twelfth century. This is really an aqueduct, though not usually so called; it is kept in repair by the present Water-Company, and is of great importance for Rome; as the floods to which the Almo was always liable along its whole line, and within the walls of Rome, (as is mentioned by Cicero,) are effectually kept out of Rome, and a constant, regular supply of water is obtained. XVIII. AQUA FELICE, made A.D. 1587 by Pope Sixtus V. (Felice Peretti).