eparated from the side aisles by arcades, the
arches of which spring from the capitals of columns; and high up in
its side walls we find windows. The side aisles, like the nave, have
wooden roofs. The nave terminates in a semicircular recess called "the
apse," the floor of which is higher than that of the general
structure, and is approached by steps. A large arch divides this apse
from the nave. A portion of the nave floor is occupied by an enclosed
space for the choir, surrounded by marble screens, and having a pulpit
on either side of it. These pulpits are termed "ambos." Below the
Church of San Clemente is a vaulted structure or crypt extending under
the greater part, but not the whole, of the floor of the main
building.

The description given above would apply, with very slight variations,
to any one of the many ancient basilica churches in Rome, Milan,
Ravenna, and the other older cities of Italy; the principal variations
being that in many instances, including the very ancient basilica of
St. Peter, now destroyed, the avenues all stopped short of the end
wall of the basilica, and a wide and clear transverse space or
transept ran athwart them in front of the apse. San Clemente indeed
shows some faint traces of such a feature. In one or two very large
churches five avenues occur,--that is to say, a nave and double
aisles; and in Santa Agnese (Fig. 156a) and at least one other, we
find a gallery over the side aisles opening into the nave, or, as Mr.
Fergusson puts it, "the side aisles in two stories." In many instances
we should find no atrium, but in all cases we meet with the nave and
aisles, and the apse at the end of the nave, with its arch and its
elevated floor; and the entrances are always at the end of the
building farthest from the apse, with some sort of porch or portal.

[Illustration: FIG. 156a.--BASILICA, OR EARLY CHRISTIAN CHURCH OF
SANTA AGNESE AT ROME.]

The interest of these buildings lies not so much in their venerable
antiquity as in the fact that the arrangements of all Christian
churches in Western Europe down to the Reformation, and of very many
since, are directly derived from these originals. If the reader will
refer to the description of a Gothic cathedral in the companion volume
of this series,[28] it will not be difficult for him to trace the
correspondence between its plan and its general structure and those of
the primitive basilica. The atrium no longer forms the access to a