[Illustration: FIG. 138.--THE CORINTHIAN ORDER FROM THE PANTHEON,
ROME.]

_Bridges and Aqueducts._

The earliest Roman bridges were of wood, and the Pons Sublicius,
though often rebuilt, continued to be of this material until the time
of Pliny, but it was impossible for a people who made such use of the
arch to avoid seeing the great advantage this form gave them in the
construction of bridges, and several of these formed of stone spanned
the Tiber even before the time of the Empire. The finest Roman
bridges, however, were built in the provinces. Trajan constructed one
over the Danube which was 150 ft. high and 60 ft. wide, and the arches
of which were of no less than 170 ft. span. This splendid structure
was destroyed by his successor, Hadrian, who was probably jealous of
it. The bridge over the Tagus at Alcantara, which was constructed by
Hadrian, is another very fine example. There were six arches here, of
which the two centre ones had a span of 100 ft.

The Roman aqueducts afford striking evidence of the building
enterprise and architectural skill of the people. Pliny says of these
works: "If any one will carefully consider the quantity of water used
in the open air, in private baths, swimming-baths, houses, gardens,
&c., and thinks of the arches that have been built, the hills that
have been tunnelled, and the valleys that have been levelled for the
purpose of conducting the water to its destination, he must confess
that nothing has existed in the world more calculated to excite
admiration." The same sentiment strikes an observer of to-day when
looking at the ruins of these aqueducts. At the end of the first
century A.D. we read of nine aqueducts in Rome, and in the time of
Procopius (A.D. 550) there were fourteen in use. Of these, the Aqua
Claudia and the Anio Novus were the grandest and most costly. Those
were constructed about the year 48 A.D., and entered the city upon the
same arches, though at different levels, the Aqua Claudia being the
lower. The arches carrying the streams were over nine miles long, and
in some cases 109 ft. high. They were purely works of utility, and had
no architectural decorations; but they were most admirably adapted for
their purpose, and were so solidly constructed, that portions of them
are still in use. Some of the provincial aqueducts, such as those of
Tarragona and Segovia in Spain, were more ornamental, and had a double
tier of arches. The Pont du Gard, not far