In bonding their stone they employed various methods, including those of the Greeks. Of these, a favourite one was the building of exterior faces only, and filling up the intervening space with broken stone and mortar. In order to produce the greatest effect at the least cost, in the use of marble, they resorted to panelling the external surfaces only with thin slabs. Interiors were lined with stucco and frequently ornamented with paintings, and the floors inlaid with mosaic. Roman mouldings were sections of the sphere, differing from the Greek, which were hyperbolas or parabolas. The chief constructions of the Romans were houses, temples, palaces, amphitheatres, theatres, aqueducts, sewers, baths, triumphal arches, tombs and commemorative structures, camps, bridges, and basilicas. [Illustration: PALACE OF DIOCLETIAN AT SPALATRO. (_From Durand._)] In, and in close proximity to, the Forum Romanum, or Campo Vaccino, are admirable examples of nearly all these different buildings. The level of the ancient market-place is several feet below that of the streets of modern Rome, but in the excavated portions are to be seen the old pavements of irregular stone slabs, laid upon concrete foundations and worn with the wheels of chariots. Many ruined temples, the arches of Septimius Severus, of Titus and Constantine, the palace of the Cæsars, the Colosseum, and the Baths of Constantine are collected here within a stone’s throw. By taking up each class of buildings separately, however, we will get a better idea of the nature of Roman architecture than by a description of isolated buildings. Roman houses resembled in a measure the Greek, the different apartments being grouped around inner courts. The rooms consisted of halls, vestibules, banqueting-rooms, and sleeping-chambers, the women not being separated from the men, as was the case in Greece. The courts were surrounded by colonnades and in the centre a well was usually placed, to receive the water from the roofs. Many of the houses were several stories in height, but a limit to their altitude was fixed by decree. The excavations in Pompeii have uncovered many interesting specimens of private dwellings, richly decorated with several paintings and having elaborate mosaic patterns on their floors. In the city of Rome the palace of the Cæsars was the most notable example of domestic architecture, but at the present day it is difficult to discern among the débris and fallen walls what its original plan may have been. Some paintings in the so-called house of Livia, upon the plateau of the palace, however, show that the artists of the period had attained a high degree of merit. [Illustration: PLAN OF THE PANTHEON AT ROME]