For the last half-mile, the Claudian arcade was also the boundary of the palace gardens of the Sessorium, the residence first of the Kings and afterwards of one branch of the imperial family (that of Verus or Varius), who resided there for more than a century. That portion of the arcade still exists for a considerable extent, forming the northern wall of that garden, and at the same time part of the wall of the city, Aurelian having adopted it, and incorporated it with his great wall. This portion is thoroughly shewn in my Photographs, as it is a very important part of the antiquities of Rome, and illustrates many points. It was the place where the principal aqueducts entered Rome, and the whole ground is full of remains of them with their reservoirs and filtering-places. The inner side of the wall is the part necessarily shewn, because the outer side is concealed by the arcade of the Aqua Felice, excepting in places where the _specus_ of the Claudia and the Anio Novus appear above it. Just outside of this garden, at the west end of it, is the great foss which separated the Sessorium, or fortified palace, from the other fortifications of the City, and in it are remains of the two great reservoirs that were probably the Gemelli or Twins of Frontinus, made originally for the Appia and the Anio Vetus side by side, and used afterwards to receive the surplus water of the later aqueducts on a higher level. We then have a considerable number of the Arches of Nero, following a straight line for another mile to the west end of the Cœlian Hill; where remains of the great reservoir are on a level with the _specus_ carried on the top of this arcade, fifty feet above the ground in that high situation, from which the water was distributed in all directions, first on other arcades, three of which branched off from this point, and afterwards in metal pipes when it was sub-divided; but for the main supply no metal pipes then to be had were large and strong enough to bear the pressure of a stream of water four feet deep and two feet wide, running at the rate of five or six miles an hour, if not more. The direct line went on over the Palatine to the Capitol, passing over the Forum Romanum on the bridge of Caligula, of which, also, some remains are shewn in my Photographs; the other two branches from the great reservoir over the Arch of Dolabella, went one to the right to the Colosseum (to supply the Stagna there), the other to the left to the Aventine, to supply the private house of Trajan and the Thermæ of Sura.