differed in other respects, agree in this--that the openings, be they
doors, or be they spaces between columns, were spanned by beams of
wood or lintels of stone (Fig. 1). Hence this architecture is called
architecture of the beam, or, in more formal language, trabeated
architecture. This mode of covering spaces required that in buildings
of solid masonry, where stone or marble lintels were employed, the
supports should not be very far apart, and this circumstance led to
the frequent use of rows of columns. The architecture of this period
is accordingly sometimes called columnar, but it has no exclusive
claim to the epithet; the column survived long after the exclusive
use of the beam had been superseded, and the term columnar must
accordingly be shared with buildings forming part of the succeeding
series.

[Illustration: FIG. 1.--OPENING SPANNED BY A LINTEL. ARCH OF THE
GOLDSMITHS, ROME.]

The second great group of buildings is that in which the semicircular
arch is introduced into construction, and used either together with
the beam, or, as mostly happened, instead of the beam, to span the
openings (Fig. 2). This use of the arch began with the Assyrians, and
it reappeared in the works of the early Etruscans. The round-arched
series of styles embraces the buildings of the Romans from their
earliest beginnings to their decay; it also includes the two great
schools of Christian architecture which were founded by the Western
and the Eastern Church respectively,--namely, the Romanesque, which,
originating in Rome, extended itself through Western Europe, and
lasted till the time of the Crusades, and the Byzantine, which spread
from Constantinople over all the countries in which the Eastern (or
Greek) Church flourished, and which continues to our own day.

[Illustration: FIG. 2.--OPENING SPANNED BY A SEMICIRCULAR ARCH. ROMAN
TRIUMPHAL ARCH AT POLA.]

[Illustration: FIG. 3.--OPENINGS SPANNED BY POINTED ARCHES. INTERIOR
OF ST. FRONT, PERIGUEUX, FRANCE.]

The third group of buildings is that in which the pointed arch is
employed instead of the semicircular arch to span the openings (Fig.
3). It began with the rise of Mohammedan architecture in the East, and
embraces all the buildings of Western Europe, from the time of the
First Crusade to the revival of art in the fifteenth century. This
great series of buildings constitutes what is known as Pointed, or,
more commonly, as Gothic architecture.