§ 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.
[Illustration: Fig. 2. Plan of San Vitale, Ravenna: (1) _narthex_ with flanking turrets, as originally arranged; (2) central nave; (3) chancel and altar.]