The relation of the wall to the configuration of the height on which Pompeii stood was pointed out in connection with our general survey of the city (p. 31). Along the southwest side, at the time of the eruption, it had almost completely disappeared. Here, where the slope was steepest and the city best defended by nature, the wall had been removed, and its place occupied by houses, at a comparatively early date, probably in the second century B.C.; enough fragments remain, however, to enable us to determine its location with certainty. Elsewhere the greater part of the wall is in a fair state of preservation. The towers did not belong to the original structure, and one of the gates in its present form is of still more recent origin. The construction of the wall will be readily understood with the help of the accompanying illustrations. First, two parallel stone walls were built, about 15 feet apart and 28 inches thick; both walls were strengthened on the side toward the city by numerous buttresses, the inner wall being further supported by massive abutments projecting into the space between (Fig. 108). This space was filled with earth. When the desired height, 26 or 28 feet, was reached, a breastwork of parapets was constructed on the outer wall; the inner wall was carried up about 16 feet above the broad passageway on the top (Fig. 110) as a shield against the weapons of the enemy, preventing the missiles from going over into the town and causing them to fall where the garrison could easily pick them up to hurl back again. Rain water falling on the top flowed toward the outside, and was carried beyond the face of the masonry by stone waterspouts. [Illustration: Fig. 108.--Plan of a section of the city wall. A. Inner wall with buttresses and abutments. B. Outer wall. C. Filling of earth between the stone walls. D. Tower. E. Stairs leading to the top of the wall.] For additional strength there was heaped against the inner wall an embankment of earth, which still remains on the north side, between the tenth and twelfth towers. At the right of the Herculaneum Gate the place of the embankment and of the inner wall was taken by a massive stairway (E in Fig. 108) leading to the top. Originally, the stairs extended east about 270 feet, but afterwards they were demolished for the greater part of the distance, and houses were built close to the wall. There is a smaller stairway of the same kind east of the Stabian Gate (Fig. 111).