Father Mullooly, the excellent Prior of S. Clement, says he has observed that the water under this church always rises and falls at the same time as that under the Colosseum, and he is convinced that they both come from the same source. It seemed probable that this source, or at least one of the sources of this water, is the great reservoir of the earliest aqueduct, the Aqua Appia, under the garden of the Villa Cœlimontana, formerly called Villa Mattei, which is now the property of the Baron Hoffman, at the west end of the Cœlian Hill, on a high level. The Baron wanted to make this old vaulted reservoir into a wine-cellar, but found it impossible to get rid of the water, which is always two or three feet deep, and as fast as he pumped it out it filled again to the same level, but no higher; this shews that there must be some outlet to it, but so deep underground that no one knows which way it goes. This old reservoir is nearly under the great reservoir of Nero for the Anio Novus, which was fifty feet higher, and carried on his arches, for which also the Arch of Dolabella was used as a substructure only. We have found in our examination of the aqueducts that the later ones always followed the same course as the earlier ones, not exactly over them, but by the side of them, each succeeding aqueduct being always on a higher level, and there is always a subterranean reservoir of one of the earlier aqueducts nearly under those of the later period. The Appia was made nearly four centuries before the Anio Novus, still it is very probable that the same plan was followed in both cases. We have found that the aqueduct of Claudius and Nero, called the Anio Novus, was divided into three branches at this point; one went straight on over the Palatine to the Capitoline Hill, another branch went to the left, or south, of the Aventine, and a third to the right, or north, to the Colosseum. It seems extremely probable that the same plan had been followed with the Appia, both were carried along the high ground of the Cœlian Hill as far as could be done, and then each was divided into three branches. We traced one branch of it over the Porta Capena to the Aventine and the Tiber; this is now necessarily out of use, the gate on the arch of which it was carried having been destroyed. A landslip in the garden of the Marchese Rappini, in February, 1876, between the Villa Cœlimontana and the Palatine, served to shew that a _specus_ or conduit passed there, now also out of use. An excavation was made there in April of the same year, but all that came to light was a deep well, an ancient quarry of tufa, also at a great depth, and the _specus_ of the aqueduct coming from the reservoir under the Claudium, called a _vivarium_, and going in the direction of the valley in which was the Porta Capena. This _specus_ has been long out of use, and could not have had any connection with the flood in the Colosseum, which was the object of the search. The water