conveyed in this _specus_ originally must have been one of those that passed over the short _agger_ of Servius Tullius from the Cœlian to the Aventine, found in the excavation of 1868, and traced also in 1876 in the cave under S. Sabba, by the side of the Aqua Appia, in the same tunnel, but in a terra-cotta pipe, not in the stone _specus_. The third branch, in the direction of the Colosseum, may still be in use, though so deep as to be unknown, supplying wells only, and this may be the one tapped by the workmen employed by Signor Rosa, and which now floods the Colosseum, and S. Clement’s also. The only outlet from a large reservoir, in which the water is always three feet deep, must afford a very abundant supply of water, and the account given by the workmen who made this branch of it agrees with this. They say it was a steady constant stream of water, and it did not gush out of the earth in the manner that a natural spring does; the spring must therefore be at some distance. If this view is correct, it would be comparatively easy to turn the stream into a drain under the Clivus Scauri, and into the one made by the Municipality about 1865, under the road near the church of S. Gregory, between the Cœlian and the Palatine, and to carry it in that manner to the Tiber. It is however probable that this spring alone, which was only a subsidiary spring to the Appian aqueduct, is not sufficiently abundant to supply the quantity of water, which now rises to the height of about ten feet, or quite three metres, in the substructures of the Colosseum. There is another spring, or perhaps more than one, in the ancient stone quarry under the garden of the monks of SS. John and Paul, on the other side of the Clivus Scauri, on the site of the Claudium, or that square part of the Cœlian Hill which is nearest to the Colosseum. This site is marked on an old plan of Rome, of the sixteenth century, as a reservoir of water, and there are no less than ten wells that descend into this old stone quarry. In the eighteenth century, and down to the middle of the nineteenth, this was called a _vivarium_, and was supposed to be the place where the wild animals were kept for exhibitions in the Colosseum, but there is no visible communication from one to the other. A plan of the old quarry, which was made for this work some years since, shews that this was not a _vivarium_. There are three ponds, but perhaps only one spring of water in it, and if the outlet for this water was stopped, the whole of the quarry, or caves as they are called, would soon be full of water. It seems probable that this is the place from which the greater part of the water comes that floods both the Colosseum and the cave of Mithras, nearly under the church of S. Clement. It seems also quite practicable to remove the water by an iron pipe into the drain under the road between the Cœlian and the Palatine, made by the Municipality about 1866. The level of the quarry is eight metres above that of the