The Aqua Appia (I.) is at so great a depth near the Porta Maggiore (which stands on very high ground), that it is difficult to trace it, but the _specus_ was found in making the railway in a deep cutting about half-a-mile outside of that gate, and was described in the _Bulletino di Correspondenza Archæoligia_ at the time it was found. There is reason to believe that it entered Rome under the wall on the north side of the Sessorian Gardens, and was received in a reservoir, of which there are remains at a considerable depth, especially the lower story. This is near the reservoir of the great Basilica or Hall of the Palace, of which the apse remains. The plan and section of this reservoir are shewn in this diagram. The _specus_ from this point turned to the west, and passed along the Cœlian Hill at a low level, nearly under the arches of Nero; but before arriving at these, it passed through another large and deep reservoir to the south of the Porta Maggiore, now in a vineyard, with another large reservoir close to it. These two are believed from the situation to be the Gemelli of Frontinus. An inscription was found on the one in the garden of the Sessorium relating to the Thermæ of S. Helena, who resided in that palace, and probably the water for her bath-chambers was taken from this reservoir. PLATE VI. II. ANIO VETUS. [Illustration: VI. THE AQUEDUCTS.—ANIO VETUS. RESERVOIR NEAR THE PORTA FURBA. A. SECTION, SHEWING THE DEPTH UNDERGROUND. B. PLAN OF THE TWO CHAMBERS AND THE ENTRANCE.] The reservoir, of which the plan and section are given in this plate, is situated at about a quarter of a mile from the Porta Furba, near the junction of the old Via Latina with the Via Appia Nova. It is just two miles from Rome, and so agrees with the text of Frontinus. It seems clear that at this point part of its water was carried by the Octavian _specus_ to the Porta Maggiore, while the main stream went on along the side of the Via Appia Nova to the Asinian Gardens, just within the Porta Asinaria. It was shewn in some excavations made under my direction in 1871. We had long been looking for it, and the gardener informed us that there was a vaulted chamber under part of that garden or vineyard, where we found it, a few feet underground, and about a hundred yards from the arcade of the great aqueduct on the southern side, nearer to the present road than the reservoir. PLATE VII. LOCH IN THE AQUA JULIA, NEAR THE IMPERIAL VILLA, CALLED THE SETTE BASSI (SEPTIMIUS BASSUS?). [Illustration: VII. THE AQUEDUCTS. A LOCH IN THE AQUA JULIA, NEAR THE VILLA CALLED SETTE BASSI. PLAN AND SECTION. A. SECTION OF THE BRANCH. B. THE SPECUS. B. PLAN, SHEWING THE DIVISION AND THE LOCH. A. A. THE SPECUS. B. THE LOCH FOR THE BRANCH.]