On entering Rome, this main stream went straight on through the great bank to the large reservoir on the inner side. The reservoirs for the Tepula and Julia were much to the north, near the Porta di S. Lorenzo (the Porta Viminalis of Frontinus), as we have seen; that of the Marcia was much closer to the Porta Esquilina. The two great reservoirs, called by Frontinus the Gemelli, were made in the great foss between the Sessorium (S. Croce) and the Cœliolum (the Lateran). They had probably been originally made for the Aqua Appia and the Anio Vetus, being both at a low level, though one was much deeper than the other. Advantage was taken of these ancient reservoirs to erect the higher one required for the reception of the waters of the Claudia and Anio Novus over it, or by the side of it, as was very usual throughout Rome. The later reservoirs are always made nearly over the old ones. This is equally the case here at the entrance into Rome and at the other end of the Cœlian. The great high reservoir of Nero is close by the side of, and really over, the great subterranean reservoir of the Aqua Appia (now under the garden of the Villa Cœlimontiana, as described in the account of the Appia). The foregoing explanation seems necessary to explain the photographs that now follow, belonging to the Arches of Nero. The first of these (No. 77) shews the junction with the Porta Maggiore; the two _specus_ that pass over that great gate are visible to the right of the photograph. The beginning of the Arches of Nero is then seen, where they have to cross the great wide and deep foss of the Sessorium, and were therefore strengthened by sub-arches, as seen in No. 76. A more close view of these arches, nearly at the same point, is seen in 66. These arches were used by the engineers of the Aqua Felice whenever they suited their purpose, and cut about or destroyed without mercy; they also made use of an old _specus_ to carry their metal pipes whenever it was convenient to do so, and the _old specus_ that ran along the Cœlian was very convenient for that purpose. 1295* is from a drawing made to shew this. The _specus_ of the Aqua Felice was first carried on the lower arches of the double arcade of Nero, the upper part of the arcade being destroyed. The metal pipes were then carried down into the old subterranean _specus_ (_the Specus Vetus_ of Frontinus). This is in the same garden or vineyard as the Gemelli, in the great foss between the Sessorium and the end of one of the banks of the Tarquins, (on which the garden of the Villa Volkonski has been made, and along which the Arches of Nero run.) A portion of the grand arcade, with the _specus_ very visible on the top of it, is shewn in 759. This is close to the Scala Santa of the Lateran; the arcade carrying the aqueduct passed along the bank on the north side of the Lateran fortress on the Cœliolum, and supplied that with water.