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 archaeologist, 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, "And Pan to Moses lent his pagan horn." Many of these relics can be traced and identified, for it may be generally presumed, for the reason already given, that none are very far removed from their original situation.