The Borghese Crater (late second century B.C.) : a fine example of the grand marble garden-ornaments produced by Neo-Attic
workshops for the wealthy villa-owners of Roman Italy. Over five feet high, it is decorated with reliefs of Dionysus and his maenads
and satyrs in a conventional classicizing style. Further, almost identical objects were found in a ship-load of objets d'art wrecked off
the Tunisian coast soon after 100 B.C.
On certain types of building concrete had a profound generative or regenerative effect. In domestic architecture it lent itself to the
high-rise tenement blocks with which Roman speculators sought to capitalize on an urban population explosion in the late second
and first centuries: the eventual conversion of rubble wall-facing into standardized pyramidal blocks laid in regular diagonal courses
(opus reticulatum) was part of the same trend, for its purpose was to streamline the building process. Concrete vaults were also
readily adopted in the architecture of baths, being both damp-resistant and fire-proof. Most important, concrete determined the
transformation of the theatre from its Greek form, set in a hillside, to the complete structural independence of the Roman version.
This process was gradual, and we know many examples of intermediate phases, with auditoria constructed wholly or partly on
artificial mounds, or supported by substructures which were filled with earth; but by 55 B.C. the mature type, in which the
substructures formed a network of passages to facilitate the circulation of the audience, was embodied in the first stone theatre in
Rome, that of Pompey (above, p. 473).