which one cannot indeed any more call a lake, with stagnant pools, as in our “turf-moors.” The work which the Romans executed is wonderful. The tunnel is entire to this day, and is in length 2,700 paces, half a German league:[116] the water of the lake is diminished to an appropriate level. This alone is a considerable advantage, although the country about is now uncultivated, and has nothing but brushwood growing upon it. More important, however, is the fact that drinkable water was gained by it; as the campagna of Rome was much in want of water, and although that of the lake is by no means good, yet it is better than what is found in the wells thereabouts. The work is equal to the greatest Etruscan ones: the entrance from the lake is a vault, executed in the grandest style like the hall of a temple, and we see that Rome now built again on as vast a scale as under the kings. This is characteristic of the time of Camillus. The tunnel is most of it cut through a hard mass of lava, a small portion only through _peperino_, which is more easily worked; it is a gallery nine palms high, and five palms broad. By this means the lake is kept, probably for ever, to a fixed level: moreover, the _emissarius_ never needs to be repaired. The lake was at that time about a hundred feet above the level to which it was let off. How such a work was accomplished, is a very interesting question. If we consider the imperfect state of the instruments of those days when the use of the compass was not yet known, the task of finding the correct level at a distance of half a mile is indeed immense; nay it would even now be fraught with considerable difficulty, as one must know to a line, how high one ought to build in order to have a gradually inclined way for the water. It is known in the country, and stated in some books, that from the lake to the lower point to which the water was to be led, open shafts are everywhere seen to this day by which people even now go down to clean the _emissarius_: these did not serve merely to carry off the mud,--the lake is not muddy,--but also to calculate the depth, and to allow the air to come in. By the salt-water of the shafts, they were able accurately to calculate the line to its extremity. Now-a-days people are so little practised in levelling, that to a very recent period it was not known that the lake of Nemi lies higher than that of Alba. By sinking shafts, it was also possible for a greater number of people to work, and to bring the whole to a speedy completion: from each of them two parties might proceed till they mutually met. In this manner the tunnel was finished to the edge of the lake. The entrance was no doubt effected by a stone bore of the size of the tube of a tobacco pipe; for a wall of basalt needs not to be thicker than two ells for it sufficiently to withstand the whole pressure of the lake. An opening was made by which the lake sank gradually, so that