This great building of Scaurus was three storeys high. On the level of the ground were marble columns by the hundred, on the first floor glass columns (the only instance on record), on the upper floor they were of gilt wood. Pliny says that part of this insane work was only calculated to be of a _temporary_ character, and it was in fact all destroyed by fire a few years afterwards, and the glass columns perished equally with those of gilt wood; he also adds that other parts were calculated to be _eternal_, and this equally applies to the part we have remaining, the great substructures, which being underground, and built of large blocks of tufa, would last as long as the hills if let alone. Many of these great blocks of tufa appear to have been used a second time; they were most probably brought from the second wall of Rome, which enclosed the two hills (the Capitoline and Palatine) in one City, and therefore must have passed under the south end of the Palatine, close to this great amphitheatre. Immediately in front of it, and separated from it only by a paved street, the south end of the Summa Sacra Via is supported by a rough concrete wall of the time of Sylla, and on the surface of this concrete wall there are impressions of large blocks of tufa in the plaster with which the concrete is covered. It is well known that Roman mortar is often harder and more durable than stone. A few of the large blocks of tufa also remain in their places, where they were necessary to carry the vault of the platform above. These tufa blocks were used under the _podium_ at the bottom, to the height of twenty feet, and parallel to them is another wall of the same kind, with just room enough for a narrow passage between them[3]. In these walls, on both sides, are vertical grooves, evidently for lifts to be pulled up and let down, and larger apertures at intervals for the counter-weights.