‹‹‹ Vitr. 8.6.13 | Table of Contents | Vitr. 8.6.15 ›››
14If the soil be hard, and there be no veins of water found at the bottom, we must then have recourse to cisterns made of cement, in which water is collected from roofs and other high places. The cement is thus compounded; in the first place, the purest and roughest sand that can be had is to be procured; then work must be of broken flint whereon no single piece is to weigh more than a pound, the lime must be very strong, and in making it into mortar, five parts of sand are to be added to two of lime, the flint work is combined with the mortar, and of it the walls in the excavation are brought up from the bottom, and shaped by wooden bars covered with iron.
14But if the ground is hard, or if the veins lie too deep, the water supply must be obtained from roofs or higher ground, and collected in cisterns of “signinum work.” Signinum work is made as follows. In the first place, procure the cleanest and sharpest sand, break up lava into bits of not more than a pound in weight, and mix the sand in a mortar trough with the strongest lime in the proportion of five parts of sand to two of lime. The trench for the signinum work, down to the level of the proposed depth of the cistern, should be beaten with wooden beetles covered with iron.