against the side of the piers of the old ones, sometimes on the Marcian, as may be seen at the place called _Sette Bassi_, and near the Porta Furba, sometimes against the Claudian as near Rome. After bringing it into the city in this canal of rough stone, the water was carried in leaden pipes into the old subterranean channels, as may still be seen in the deep _specus_ on the Cœlian, and the metal pipes pass through the tall brick piers of the arcade of Nero, and are supported on flat arches across from one pier to the other, with a rapid descent over the first or ancient road from S. Croce to the Porta Maggiore, and into the Specus Vetus underground, before arriving at the second or modern one from S. Croce to S. Maria Maggiore. The point of descent is marked by a respirator. Pantano is about two miles from Gabii, and this reservoir is still in use. It is very near to the ancient _castellum aquæ_, which was made originally by Hadrian[200] for his aqueduct, as is shewn by an inscription found there. The other streams coming from Tivoli are said to have emerged also near this point, and the first engineer of the Felice, Matteo da Castello, considering the Claudian and Marcian lines as the best, followed those to the _piscinæ_; but having made a mistake in the levels, instead of using the Marcian _specus_ and arcade from the _piscinæ_ into Rome, and merely repairing it as the Pope had intended, Fontana was obliged to rebuild it entirely of the materials of the old Marcian arcade, with the help also of those of the Claudian, all the way to Rome. This was done in great haste and in a very clumsy manner[201].