But towards the close of the Republican period, Rome began to be distinguished for the magnificence of its public monuments. As its area of conquest spread, so did its luxury increase. New divinities were introduced from foreign countries, and domesticated in the Capitol; and these required more sumptuous fanes than those with which the native deities had been contented. The brown tufa of the Tarpeian Rock sufficed for the rude sanctuary of Vesta, the primitive hearth-stone of ancient Rome; but in the reconstruction of the sumptuous temple of Jupiter Capitolinus, which marked the grandest period of Roman history, the most precious stones of Asia and Africa were employed. Statues were imported wholesale from Greece to adorn temples and theatres, constructed after the models of Greek architecture, with pillars, friezes, and floors of precious Pentelic and Sicilian marble. During the last century of the Republic marble became a common building-stone. The tomb of Cæcilia Metella, and the temples of Ceres, Juno Sospita, and Castor and Pollux, indicate the introduction of this precious and beautiful material. But it was reserved for the period of the Empire to complete the architectural glories of the city. Travertine, usually called Lapis Tiburtinus, a straw-coloured volcanic limestone excavated in the plain below Tivoli, which has the useful property of hardening on exposure, was now used as the principal building-stone instead of the former lavas and tufas; and the Colosseum, entirely constructed of travertine, which was treated in the middle ages as a quarry, out of which were built many of the palaces and churches of Rome, attests to this day the beauty and durability of this material. Quarries of crystalline marbles, admirably adapted for the purposes of the sculptor and architect, were opened in the range of the Apennines overlooking the beautiful Bay of Spezia, in the vicinity of Carrara, Massa, and Seravezza, and largely worked in the time of Augustus. This emperor could boast that he had found Rome of brick, and left it of marble. The marbles of each new territory annexed to the Empire were brought at enormous expense into the Imperial City. A quay, to which reference has already been made, was constructed at the broadest part of the Tiber, where the vessels that transported marbles from Africa, and from the most distant parts of Eastern Europe and Western Asia, landed their cargoes. Here numerous blocks of marble were lately found, one of which was identified as that sent to Nero from a quarry in Carinthia; and another, a column of even more colossal dimensions, weighing about thirty-four tons of valuable African marble, was meant to serve as a memorial pillar of the Council of 1870 on the Janiculum, but the intention was never carried out. So abundant was marble during the first two centuries of the Empire, that it was nothing accounted of. Every temple, palace, and public edifice was built of it either in whole or in part. The tombs that lined the Appian Way on either side for fifteen miles had their brick cores covered with marble slabs; and their magnificence must have impressed every visitor who entered the Imperial City through this avenue of architectural glory shrouding the decays of death. It is obvious, then, that by studying the history of the conquests of Rome, the student can ascertain at what period a particular kind of marble was introduced from its native country, and the proximate date of the building in which this marble had been used.

It was a fortunate circumstance for the preservation of the precious marbles of Rome that Christianity laid its cuckoo egg in the nest of the Pagan city. When the capture of Rome by Alaric gave the final blow to heathen worship, by the overthrow of the ruling classes, who alone cherished the proud memories of the ancient faith, the greater number of the temples were still standing without any one to look after the edifices or maintain the religious services. The Christians were therefore free to take possession of the deserted shrines; and they speedily transferred to their own churches the columns and marble decorations that adorned the temples of the gods. Many of the precious stones that once beautified the palaces of emperors and senators were employed to form the altars and the mosaic flooring of the memorial chapels. Almost all the early churches were constructed on or near the sites of the temples, so that the materials of the one might be transported to the other with the least difficulty and expense, just as the settler in the back-woods of America erects his log-house in the immediate vicinity of the trees that are most suitable for his purpose. And the striking contrast between the plain, mean exteriors of the oldest Roman churches—rough, time-stained, and unfinished since their erection—and their gorgeous interiors, with their forests of columns separating the aisles, and the series of richly-sculptured and brilliantly-frescoed chapels, all blazing with gold and marble,—a contrast that reminds us of the surprising difference between the outside of a common clumsy geode lying in the mud, and the sparkling crystals in the drusic cavity at the heart of it,—would lead us to infer that the outer walls were raised in haste to secure the valuable materials on the spot, before they could be otherwise appropriated. Marangoni, a learned Roman archæologist, mentions thirty-five churches in Rome as all raised upon the sites and out of the remains of ancient temples; and no less than six hundred and eighty-eight large columns of marble, granite, porphyry, and other valuable stones, as among the relics of heathen fanes transferred to sacred ground within the city, when the bronze Jupiter was metamorphosed into the Jew Peter,