probably were places reserved for distinguished persons, near the platform of the altar. (8) West of the transept, entered by a tall and wide arch, was the apse. Beneath the arch was a screen, formed by a row of columns, under an entablature which bore statues of our Lord and the apostles: this crossed the arch at the foot of the steps leading to the altar and seats of the clergy. (9) Beneath the altar platform, and entered by doorways on each side of the flight of steps, was the crypt or confessio, the traditional place of martyrdom of St Peter, and the resort of pilgrims to the tomb of the apostles. The hallowed place was immediately beneath the altar.

§ 5. The sixth century basilicas of Ravenna, Sant' Apollinare in Classe and Sant' Apollinare Nuovo, differ in plan from the Roman basilicas (1) in the fact that they have always had the altar at the east, and the entrance at the west end; (2) by substituting, for a colonnaded atrium, a closed porch or narthex in front of the entrance of the building. In process of time, two of the greater Roman basilicas, San Paolo and San Lorenzo fuori le Mura, were enlarged in a westward direction, so that the positions of the altar and entrance were reversed; and, in several of the early basilicas at Rome, a space near the entrance of the nave was screened off, from which penitents and catechumens might watch the service. But, in the first instance, the eastern chancel and the structural narthex appear to have been introduced from the eastern empire. Neither at Ravenna nor at Rome did bell-towers originally form part of the plan of the basilica: the round campanili of both churches at Ravenna are certainly later additions. It may also be noted (1) that ordinarily the aisles were single, not double as at old St Peter's. (2) The columned screen of the apse at old St Peter's appears to have been exceptional. The ordinary screen or cancelli, from which is derived our word "chancel" for the space thus enclosed, was a low wall. This is the arrangement at the basilica of San Clemente, in which the enclosed quire also remains. (3) The transept, even in Rome, was an exceptional arrangement, and does not appear in the basilicas of Ravenna.

§ 6. Another type of plan, however, was used in Rome for churches devoted to the special purposes of burial and baptism. In this case the buildings were planned round a central point, and at Rome were uniformly circular. Recesses round the walls of the mausoleum-church contained sarcophagi: in the centre of the baptistery was the great font. The church of Santa Costanza, outside the north-eastern walls of Rome, circular in plan, with a vaulted aisle surrounding the central space, was built by Constantine the Great as a tomb-church for his family, and was also used as a baptistery. Both these uses were direct adaptations of pagan customs. The baptistery, with its central font for total immersion, was simply a large bath-room, like the great rotunda of the baths of Caracalla. The mausoleum preserved the form of which the finest example is the tomb of Hadrian, now known as the castle of Sant' Angelo. In the course of the middle ages, certain tomb-churches in Rome, with a centralised plan, were turned into places of public worship. But, for the plan of the ordinary church, the basilica, with its longitudinal axis, was general. In the eastern empire, on the other hand, the centralised plan was employed from an early date for large churches; and in this way was evolved the magnificent style of architecture which culminated in Santa Sophia at Constantinople. Here the centralised plan was triumphantly adapted to the internal arrangements of the basilica.

§ 7. The city of Ravenna, closely connected historically both with Rome and Constantinople, contains a series of monuments which is of unequalled interest in the history of the centralised plan. (1) The mausoleum of the empress Galla Placidia, sister of the emperor Honorius, who died in 450 A.D., is a building of cruciform shape, consisting of a square central space covered by a dome, with rectangular projections on all four sides. The projection through which the building is entered is longer than the others, and the plan thus forms the Latin cross so common in the churches of the middle ages. (2) To the same period belongs the octagonal baptistery, known as San Giovanni in Fonte. (3) In 493 A.D. Theodoric the Ostrogoth obtained possession of Ravenna. To the period of his rule belongs the Arian baptistery, also octagonal, known as Santa Maria in Cosmedin. (4) Theodoric died in 526 A.D. His mausoleum is formed by a polygon of ten equal sides, with a smaller decagonal upper stage, a circular attic above which bears the great monolithic dome. In the lower story was the tomb: the internal plan is a Greek cross, i.e. there is a central space with recesses of equal depth on all four sides. (5) In the year of the death of Theodoric, the octagonal church of San Vitale was begun. It was consecrated in 547, when Ravenna had become the capital of the Italian province of Justinian's empire. Its somewhat complicated plan was clearly derived from an eastern source, but not from Santa Sophia, which was not begun till 532 A.D. The central space is almost circular. Between each of the piers which support the octagonal clerestory at the base of the cupola is an apsidal recess, with three arches on the ground floor opening into the encircling aisle, and three upper arches opening into the gallery above the aisle. On the east side of the central space this arrangement is broken, and one tall arch opens into the chancel, which ends in a projecting apse, semi-circular inside, but a half octagon outside. The aisle with the gallery above thus occupies seven sides of the outer octagon, the eighth side being occupied by the western part of the chancel.