‹‹‹ Vitr. 2.8.2 | Table of Contents | Vitr. 2.8.4 ›››
3We may see this in several monuments about the city, which have been built of marble or of stones squared externally; that is, on the face, but filled up with rubble run with mortar. Time, in these, has taken up the moisture of the mortar, and destroyed its efficacy, by the porosity of the surface on which it acted. All cohesion is thus ruined, and the walls fall to decay.
3This we may learn from several monuments in the environs of the city, which are built of marble or dimension stone, but on the inside packed with masonry between the outer walls. In the course of time, the mortar has lost its strength, which has been sucked out of it by the porousness of the rubble; and so the monuments are tumbling down and going to pieces, with their joints loosened by the settling of the material that bound them together.