Sec. 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. Sec. 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