A colossal engineering problem arose because the Palazzo Fiano rested upon wooden piles driven into the water which in this part of Rome underlies most of the buildings. These piles, and reinforcements to them, pinned down some of the marble blocks of the altar itself. To get the blocks out by ordinary methods, even if the water level had made it possible, would have caused the collapse of the building. Previous excavators had resorted to driving narrow, damp, dark tunnels, with incomplete results. Moretti resolved on more heroic measures; the solution is a credit to modern Italian engineering. The weightiest and worst-supported part of the palace lay directly over the altar; there were deep splits in the palace walls; only the extraordinary tenacity of the _pozzolana_ mortar held them together. With infinite capacity for taking pains, the damaged parts of the walls were taken down and, by injection of liquid concrete, restored segment by segment, brick by brick. (The Italians call this process _cuci e scuci_, sew and unsew.) The subsoil was so uneven in profile and so soaking wet that a new masonry substructure was impossible. Moretti, in consultation with his engineers, determined to shift the weight of the palace wall onto a sort of enormous sawhorse or _cavaletto_ (Fig. 6.6) of reinforced concrete. Holes were drilled sixty-five feet to a firm footing and filled with concrete; on this were built concrete piers to support the legs of the sawhorse. Between each pier and the corresponding leg was inserted a hydraulic jack (_martinetto_) adjustable to suit the various stresses exerted by the bearing walls. A grid of steel girders ran from pier to pier for reinforcement. [Illustration: FIG. 6.6 Rome, Altar of Peace. Plan showing how corner of Palazzo Fiano was supported and a dike frozen around the remains of the altar. (G. Moretti, _Ara Pacis Augustae_, Pl. 36)]