This double arcade crosses the valley or inner foss of the Sessorian Palace. It was built on this plan for greater strength, as the piers are of a great height. This arcade is a continuation of the one that forms the northern wall of the Sessorian gardens, in a direct line to the west, over the Cœlian to the great reservoir over the Arch of Dolabella (shewn in the last plate). The _specus_ was carried at the top, and conveyed the water of the Claudian and Anio Novus, _united_ at _the Gemelli_ (a great twin reservoir which was close to that point, and at the north-west angle of the Sessorian gardens). The Claudian as a separate water turns at a sharp angle, and goes on to the Porta Maggiore, with the Anio Novus over it, and terminated at another tower just to the north of the place where the Marcia, Tepula, and Julia pass through the wall. But they left a considerable part of their water at that angle to be united to that of the Anio Novus at the Gemelli. The lower view represents a fragment of the Aqua Marcia, as repaired and restored by Trajan, to the north of, and near the Porta Maggiore, in the vineyard in which the Minerva Medica stands, which has been the Exquiliæ, and afterwards the gardens of Mæcenas. This, which is parallel to the City wall, is joined to it a little further on. It was accidentally brought to light by some excavations in 1871, and is now buried again. PLATE XVIII. THE CLAUDIAN AND THE ANIO NOVUS, IN THE NORTH WALL OF THE SESSORIAN GARDENS, NEAR THE PORTA MAGGIORE. [Illustration: AQUEDUCTS NEAR PORTA MAGGIORE. CLAUDIA AND ANIO NOVUS IN THE WALL OF THE SESSORIUM. NYMPHAEUM OF ALEXANDER SEVERUS WHERE THE TROPHIES OF MARIUS WERE HUNG.] The wall for about a quarter of a mile is entirely made out of this arcade, with the arches filled up, but it is built upon the old earthwork of the Sessorium, probably of the time of the Kings. The arcade extends from the angle at the north-east corner, where the aqueduct entered Rome, to the north-west angle near the Porta Maggiore, which was called Porta Sessoriana, because it entered into the Sessorian gardens. The lower view represents the NYMPHÆUM OF ALEXANDER SEVERUS, WHERE THE TROPHIES OF MARIUS WERE HUNG. This is identified by a representation of it on one of the coins of that Emperor. It is commonly miscalled a Castellum of the Aqua Julia, but it is on too high a level for that water, and there is no other but the Anio Novus which is high enough; this was brought along the wall to another reservoir near the Porta Tiburtina, and then by a branch arcade to this point, where there is another large reservoir on high ground, from which the water was dispersed in different directions. One branch went to supply the great reservoir called the _Sette Sale_, which supplied the Thermæ of Titus and Trajan on the Exquiliæ, and from thence went on to the Colosseum and to the Tiber. Another branch supplied the Thermæ of Constantine, on the Quirinal. PLATE XIX.