locks of lava quarried
in the neighbourhood from the abundant deposits which had formed in a
not very remote volcanic period.

The materials employed for substantial building were various; in the
older days red and black tufa--a stone so soft as to require
protection by a layer of stucco; later the dark-brown peperino, the
golden-creamy travertine, marble white and coloured, and concrete. The
modern visitor to Rome who regards the ruins but superficially would
naturally imagine that many of the edifices were mainly constructed of
brick. In reality there was no building so composed. The flat
triangular bricks, or rather tiles, which are so much in evidence, are
but inserted in the face of concrete to cover the nakedness of that
material. Concrete alone might serve for cores and substructures, but
those parts of the building which showed were required to present a
more pleasing surface. At the date of Nero this might be achieved by a
fronting of marble slabs and blocks, but more commonly it was obtained
by means of the triangular red or yellow tiles above mentioned. In
buildings of slightly earlier date the exterior often presented a
"diamond pattern" or network arrangement of square pieces of stone
inserted in the concrete while it was still soft. The huge vaults and
arches affected by the Romans made concrete a particularly convenient
material, and nothing could better illustrate its strength than the
tenacity with which it has endured the strain in the unsupported
portions of the vaults of the Basilica of Constantine. Any of the more
imposing buildings which were not mainly of concrete were composed of
blocks of stone, held to each other by clamps soldered in with lead.
Few, if any, such buildings were made entirely of marble. In the case
of those composes of the other varieties of stone already named, the
surface was commonly coated either with stucco or with marble facings
attached by hook-like clamps fixed into the main structure Externally
the appearance of Rome--so far as its public buildings are
concerned-was that of a city of marble. The present having been for
centuries torn away, either to be used elsewhere, or more often to be
burned down for lime.

[Illustration: FIG. 28.--BUILDING MATERIALS. (From Middleton.)]

CHAPTER IX

THE ROMAN TOWN HOUSE

We have taken a general survey of the city of Rome, its open places,
streets, and public buildings. We may now look at the houses in which
the Romans