Early Christian Architecture. 59 ward from this central point to the chief entrance is called the nave (from navis, a ship) ; and the portion which runs eastward is the choir. The columns of the aisles were joined together by means of arches, or by a horizontal architrave, and the central aisle or nave was higher and wider than the side-aisles. In many cases, numbers of windows with semicircular arches were let into the walls of the nave above the columns, through which a flood of light was admitted to the body of the church. In the low walls running round the side-aisles windows were also sometimes introduced ; but the apsis or choir was generally left unlighted, in a kind of mystic twilight, produced by the reflection of the light in the rest of the building on the glimmering gold mosaics with which it was adorned. There was a separate entrance to each aisle, and in large churches the nave had three entrances. An atrium or enclosed court-yard generally existed at the entrance to the basilica; it was usually surrounded by columns, and formed an essential feature of most early churches. The earliest Christian basilicas are also most beautiful, as the costly materials of the ruins of fine antique buildings were employed in their construction. The church of St. Paul at Rome (Fig. 31), destroyed by fire in 1822, was one of the finest and most interesting of the basilicas of that city. It was built by Theodosius' and Honorius, about 386. Unfortunately it has been restored in modern style, and little remains of its original beauty. The old basilica of St. Peter, replaced in the fifteenth century by the great temple bearing the same name, was erected in the reign of Constantine, and was a magnificent structure, with a noble atrium or entrance-court, and a
