Colosseum; the soil there is on the level of the arena, and that is seven metres above the original pavement; the water in the old quarry is therefore fifteen metres, or about 45 ft. above the level of the old drain of the Colosseum, and nearly six metres above the drain made by the Municipality. This opportunity may be taken to say, that great credit is due to the Municipality of Rome for the energy and perseverance with which they have carried on an admirable system of new drainage for the city; and not only the new city on the hills on the site of the city of the Kings and of the Empire, but also of the modern city of the Popes, built in the swamp between the hills and the Tiber, the draining of which is by no means easy. Nothing can be better than the old Cloaca Maxima, which is still the chief drain to this part of Rome, or for that of part of the old city; it drains the water of the streams that run down from three hills, the Palatine, the Capitoline, and the Quirinal, on this side. But on the northern side of the Capitoline Hill, in which was the Campus Martius, the mediæval drains are by no means equally good with those of the Kings; the mouths of these drains are always open to the Tiber, and when there is a flood of the river the water runs up the drains, and the Pantheon, which stands on very low ground, is always the first place in Rome to be flooded. Surely a sluice-gate might be placed at the mouth of each drain, suspended from a bar at the top, and worked on pivots only, which would let the water out, but would not let any in, as in the common _traps_ of a drain in daily use in England. The Roman authorities say that the water of the Tiber would close the doors, and not let any of the water in the drain pass out, but if the door was placed obliquely, and let the water flow past it with as little pressure upon it as possible, the water in the drains, which runs rapidly and with considerable force, would very soon force open the door that was suspended at the mouth of it. Any embankment of the Tiber would be money thrown away; if the great engineers and architects who built the wall of Aurelian, could not make it secure on the bank of the Tiber, no modern engineers or architects will do so. We see that nearly the whole of the great wall of Aurelian, on the bank of the Tiber, has been swept away by the great floods; the substructures of the towers, under water, remain, and are visible when the water is low in the river, but all along the bank has been swept away. When the water rises at the rate of a foot in an hour, and continues to do so for twenty hours consecutively, and runs at the rate of nine or ten miles an hour, no wall can stand against it that offers any resistance to it; smooth walls parallel to the course of the river might stand, as the quay of the Ripa Grande does, because it offers no resistance to the water.