1532. Ponte Lupo, near Poli, west side, below Tivoli, the finest of all the bridges of the aqueducts. It crosses a valley from one cliff to the other, and is a solid wall for part of the way, the rest on arches. The two _specus_ are here visible, as seen from below on the west side. 687. Arrived in the valley of the Campagna, the great _piscina_ of the Anio Novus and that of the Claudia, which is near to it, is underground, and the summit of it only is visible, appearing like a tumulus. It is near the old Via Latina, and below the present roads to Albano, Frascati and Marino. 74 and 75. After leaving the great _piscinæ_, the two _specus_ are carried on the fine arcade, of which a panoramic view is here given, shewing its general effect for some miles. 554. Passing by the remains of Roma Vecchia to the Torre Fiscale and the Porta Furba (given under the head of the Aqua Claudia), the _specus_ rises to a remarkable reservoir, which from its great elevation must have belonged to the highest of the aqueducts. It is a most picturesque one, near the Mausoleum of S. Helena, but is earlier than her time; it belongs rather to that of Trajan, being faced with fine reticulated work, with layers of bricks on the exterior. The interior is distinguished by remarkably solid central buttresses, to support the wall against the pressure of the water (553). 926. Another large reservoir of the same period and style, and at nearly the same level; it occurs about a mile further from the main line of the aqueducts, at the place called Torre de’ Scavi, where the Thermæ of the Gordiani were afterwards made. This appears also to have belonged to the Anio Novus, as no other aqueduct is high enough for the water to have reached it. ARCHES OF NERO. At the great reservoir inside the Porta Maggiore (the Porta Esquilina of Frontinus), the water of the Claudia and the Anio Novus was united for the general use of the City. This aqueduct entered on the highest ground in Rome, and the water supplied the deficiencies of any of the other aqueducts in case of need. Being a part of the river Anio, it never failed. It was forced to come through Rome, as has been shewn by the arrangements in the bed of the Anio above Subiaco. This united water was carried to all the fourteen Regiones of Rome, and in order to ensure an abundant supply, it was conveyed in the great stone _specus_, on the fine arches of Nero along the whole length of the Cœlian Hill for more than a mile; at the west end of the Cœlian an enormous reservoir was built for it on the level of the _specus_ at the top of these arches, so that the base of the reservoir was fifty feet from the ground, and the road passed under it. From this great central reservoir, at a very high level, the water was distributed in various directions.