The account given of the map of the eastern side of Rome applies almost equally to this, but the difficulty to be surmounted was here greater. Neither Dr. Gori, nor Signor De Mauro, nor the author knew the ground; we had only Frontinus and Fabretti to help us, and the course is much more subterranean on this side than on the other. There are none of the great arcades to carry the _specus_ for five or six miles; the only portion where they are carried on an arcade for any distance is on the side and upon the wall of the garden of the villa Pamphili-Doria, and there the arcade as seen is the work of Pope Paul V. (Borghese), who restored them to use in the sixteenth century, making use of the old subterranean _specus_ and the ruins of the old arches, which can be seen against the wall of that garden. From this point they are mostly subterranean, we traced them to the three lakes which served as reservoirs for them. The first _specus_ on this side of the Lacus Alsietinus has been kept separate from the one on the other side. In the time of Augustus the water came from the two upper lakes, but it was brought at a very low level, and the water from these being always muddy and bad, Frontinus, under Trajan, rejected it, and brought the water only from the Sabatina; Pope Paul returned to the use of the upper lake, Alsietina. This map is also reduced by photography from one on a much larger scale, though not so large as the one for the eastern side, as that was found inconveniently large, and on this side there was less complication to examine and explain. Great credit is due to Signor de Mauro for the tact with which he traced the subterranean lines. He found that there are wells and air-holes at intervals, not always regular, but nearly so, and that when they are in grass-land or barren land, shrubs have always grown over the top of each well on account of the moisture that remained in it, and by means of these shrubs he was able to follow the line.