Roman Architecture. 53 beauty of detail, and for the fact that it commemorates the conquest of Jerusalem. The vast arch of Constantine (Fig. 27) owes much of its interest to its sculptures having been borrowed from a Trajan monument of earlier date. The tomb of Hadrian, which still exists under the name of the Mole of Hadrian, or the Castle of St. Angelo, surpasses all the sepulchral monuments of the time. Its basement was a square of about 340 feet, and 75 feet high, above which rose a round tower 235 feet in diameter and 140 feet in height, the whole being crowned by a dome, the central ornament of which was a quadriga. It was faced with Parian marble, and contained two sepul- chral chambers, one above the other. The basilica of Constantine, begun by Maxentius, belongs to the latest period of ancient art. Fragments of the broken roof are strewn like masses of rock upon the ground, but three barrel vaults, which have remained standing, still rise from the ruins, together with the apse subsequently built on to the side-aisle ; and, with the Colosseum, they overlook the desolate scene so suggestive of fallen greatness, and form a striking feature of the landscape for miles round. Of the various fora (open spaces where markets and courts of justice were held) the largest and most celebrated was the Forum Romanorum. It stretched from the foot of the Capitoline Hill to the temple of the Dioscuri, and was surrounded by temples and houses. The boundary on the east and north was the Via Sacra (Sacred Way) ; on the other sides were corridors and halls (for the bankers, money-changers, etc.), many of them of great beauty. The Forum Trajanum, erected by the architect Apollodorus, is remarkable for its great circumference, and for its simple
