3. Opus reticulatum, reticulated work; this kind of construction, also antique, consisted of small stones of peperino, or tufo, volcanic productions from the environs of Rome; they were cut into small pyramids, about three inches at the base, and five or six inches in height; they were arranged diagonally on the surface of the wall, and the points entered the general mass of rubble of which the wall was composed; there was scarcely any mortar between the joints of the reticulatum, but the whole was gencrally covered with cement. A fine example of the reticulatum is seen in part of the walls of Rome, between the Porta del Populo, and the Villa Borghese, called the Mura torto.
4. Same kind of masonry, in which there was more mortar between the lozenges, but the outer covering of cement was dispensed with.
5. Another kind of reticulatum, a gross imitation of the preceding, but with stones of unequal and irregular form, with a greater quantity of mortar between the joints.