ults close
to one another, so that large portions of the original main wall might
be dispensed with. What remained of the side walls was now only a
series of oblong masses or piers, suitably fortified so as to carry
the great weight resting upon them, but leaving the architect free to
occupy the space between them as his fancy might dictate, or to leave
it quite open. In this way were constructed the great halls of the
Thermae; and the finest halls of modern classic architecture--such, for
example, as the Madeleine at Paris, or St. George's Hall at
Liverpool--are only a reproduction of the splendid structures which
such a system of vaulting rendered possible.

When the floor of the space to be vaulted was circular, the result of
covering it with an arched roof was the dome--a familiar feature of
Roman architecture, and the noblest of all forms of roof. We possess
in the dome of the Pantheon a specimen, in fairly good preservation,
of this kind of roof on the grandest scale.

We shall find that in later ages the dome and the vault were adopted
by the Eastern and the Western schools of Christian architecture
respectively. In Rome we have the origin of both.

_The Openings._

These were both square-headed and arched; but the arched ones occur
far more frequently than the others, and, when occasion required,
could be far bolder. The openings became of much greater importance
than in earlier styles, and soon disputed with the columns the dignity
of being the feature of the building: this eventually led, as will be
related under the next head, to various devices for the fusion of the
two.

The adoption of the arch by the Romans led to a great modification in
classic architecture; for its influence was to be traced in every part
of the structure where an opening of any sort had to be spanned.
Formerly the width of such openings was very limited, owing to the
difficulty of obtaining lintels of great length. Now their width and
height were pure matters of choice, and doorways, windows, and arcades
naturally became very prominent, and were often very spacious.

_The Columns._

These necessarily took an altered place as soon as buildings were
carried to such a height that one order could not, as in Greek
temples, occupy the whole space from pavement to roof. The Greek
orders were modified by the Romans in order to fit these altered
circumstances, but columnar construction was by no means disused when
the arch came to