ped the buildings they
erected with a character of their own. From the first sun-dried bricks,
sometimes combined with stone, were the chief materials used, even the
grander structures of the best period such as the huge palaces and halls
were of plastered brickwork, stone having been as a general rule
reserved for such works as temples, theatres, and triumphal arches.
Concrete was also largely employed, and timber in many cases was turned
to account for roofing. The most distinctive peculiarity of the
architecture of the Romans is the vaulted roof, which they employed in
an infinite variety of ways, introducing it at every possible
opportunity. The simplest form, known as the waggon or barrel vault, is
a semicircular arch spanning two walls, whilst a more elaborate
contrivance consists of two intersecting vaults of the same height
crossing each other at right angles, which was used in Rome as early as
75 B.C. These two forms were sometimes supplemented by what are
distinguished as conches or half-domes over external semicircular
recesses, of which the apse is a characteristic example. With the aid of
these three varieties of vaulting, that were occasionally combined with
consummate skill, the Romans were able to roof in large or small
circular spaces, and in some few cases, as in the Baths of Caracalla at
Rome, they even to a certain extent anticipated the clever contrivance
known as the pendentive, a triangular piece of vaulting springing from
the corners of a right-angled enclosure, that was later brought to such
perfection in Byzantine architecture.

[Illustration: Intersecting Vaulting]

With their wonderful system of vaulting the Romans combined the
columnation and entablature of the Greeks, introducing innovations
however that were in many cases anything but improvements. Thus they
sometimes supplemented the foliage of the Corinthian capital with the
volutes of the Ionic; whilst what is known as the Tuscan style is really
merely a modification of the Doric, and is wanting in the simple dignity
that characterised the latter, the metopes being adorned with sculptures
very inferior to the beautiful figure subjects of the Parthenon and
other Greek temples. Roman architects were in fact rather skilful
engineers and adapters of the aesthetic conceptions of others than
original designers of new forms of beauty, but they were unrivalled in
their power of harmoniously co-ordinating in a single building an
infinite varie