Architecturally also the earliest churches resembled more nearly the domestic hall than the public basilica. The latter were little more than a covered portion of the Forum upon which they stood. They were entered from either side through the open ambulatories which as we have seen were free to all. The extremities were walled up later and prolonged into an apse to increase the space available for legal purposes. The domestic basilica on the other hand was a rectangular building roofed and closed on all sides, its single apse at one extremity facing the main entrance. The central space was surrounded on three sides by porticoes dividing it into portions which became the aisles for the worshippers and the narthex for the use of catechumens. The domestic judge's seat standing in the apse was replaced by the bishop's throne, and the cancellum became the chancel rail dividing this portion, the presbytery of the church, from the rest of the building.
The ruins of the Flavian basilica in Domitian's house on the Palatine (81-96) affords us a ground plan of such a domestic hall, in this instance placed close to the triclinium of the house and not in a direct line with the vestibulum or entrance as was generally the case. Here a fragment of the cancellum can still be seen in situ.
The Christian altar of the earliest churches placed in front of the apse, faced the congregation, and a space before it, beyond the depressed portion or confessio, was reserved for the choir and was surrounded by a marble balustrade. The columns supported a horizontal architrave, above it a flat wall pierced with windows and the plain roof of cedar-wood beams.
The floors were paved with a fine mosaic of marble and green serpentine alternating with slabs of white marble or discs of red porphyry. Tribune, arch, and vault, and sometimes other portions of the walls, were decorated with brilliant mosaics and examples of this work, of the fourth, sixth, ninth, and twelfth centuries, and possibly of the second or third, have happily escaped the ravishing hand of the restorer. In the twelfth century the art of marble working underwent a temporary revival under the influence of a talented family of artists, the Cosmati; and a good deal of their work and that of their school is still to be found in Rome, the carved marble and an inlay of mosaic upon marble being easily recognisable in the decoration of the cloisters of the Lateran and of S. Paul's outside the walls, upon ambones, candelabra, and tombs scattered throughout the churches.
The straight architectural lines of the Christian basilicas and their subdued colouring of floor and apse produce a delicate and harmonious effect, but they were erected during a debased building period and were not designed for strength, and only a few have weathered the storms of the middle ages and escaped destruction beneath the tasteless restorations of the Renaissance.
The new building epoch born in Rome was to be nourished entirely at the expense of the old. Columns and mouldings were transferred bodily from the nearest basilica to furnish the Christian church, and were there arranged haphazard. Simpler still, walls of ancient bricks were quickly run up between the solid columns of a temple; marble casings were torn off to be used as common building stone; statues, carved cornices, and friezes were thrust into lime-kilns which sprang up all over the city wherever the ancient monuments stood thickest; priceless marbles were ground into fragments for making mosaics or were mixed with cement and made into concrete.
When Constantine left Rome to found his new capital the city had already degenerated into a squalid provincial town, and fifty years later Jerome could refer to its gilded squalor and its temples lined with cobweb.
Already the seal had been put upon the old order when Gratian in 383 abolished the privileges of the pagan places of worship, and quickly disaster followed upon the heels of destruction. Twice Alaric despoiled the city and carried off priceless booty. Vitiges tore the marble from the mausoleum of Hadrian and destroyed the aqueducts; Genseric dismantled the temple of Jupiter; Robert Guiscard laid waste the Campus Martius and other parts of the city by fire. Sieges, sacks, earthquakes, fires, and inundations succeeded each other until the old level of the city was in places buried 50 feet beneath accumulated ruin and rubbish.
The scene shifts once more; centuries have slipped by and the city of Rome has become a desolation. Marble columns and granite obelisks lie prone upon the ground, and many more have found graves beneath the soil. Enormous mounds of earth and masonry, disfigured with rude battlements, represent all that is left of the great monuments; crumbling ruins and waste land stretch away to the walls, and without the campagna has become a fever-stricken wilderness.
Military fortresses, watch-towers on the walls, and bell-towers of churches are the only buildings kept in repair. Gaunt wolves snarl and fight over the refuse heaps under the walls of S. Peter's. A gibbet crowns the bare summit of the Capitol, goatherds pasture their flocks on its sides and along the green slopes of the Forum, and thus the hill and the tract of land at its foot have returned once more to their primitive pastoral state and their pastoral names, the "hill of goats" and the "field of cows." Over all broods the ominous silence of terror, bloodshed, and pestilence.