It would, however, be endless to enumerate the varied forms of domed churches in the East, though, with all their varieties, they may usually be reduced to a few elementary types. If you desire to study them, I would recommend to you Salzenberg’s _Old Christian Architecture at Constantinople_, Couchaud’s _Byzantine Churches in Greece_, and Texier and Pullan’s _Byzantine Architecture_. It is not, however, in the East alone, that the Byzantine dome is to be found, even in its earliest days--those [Illustration: Fig 431.--Plan, St. Vitale, Ravenna. (_From Fergusson._)] [Illustration: Fig. 432.--Section, St. Vitale, Ravenna. (_From Fergusson._)] of Justinian himself. It established itself equally at Ravenna; indeed, as we have seen in the baptistery there, as well as in the tomb of Galla Placidia, it, in an early form, preceded those at Constantinople itself. Its great effort, however, there, was the Church of San Vitale, erected by Justinian and Theodora (Fig. 431). This church was evidently imitated more or less from the Temple of Minerva Medica, though whether directly or through that of SS. Sergius and Bacchus at Constantinople can hardly be judged. It is a grand octagon, with a spacious surrounding aisle of double height (Fig. 432). Seven of its sides have the same circular niches projecting from them that we find in the temple (as well as in the Church of SS. Sergius and Bacchus), only they are arcaded and carried out with purely Byzantine details. The aisles are of two storeys, united behind a lofty arcade. This is surmounted by a clerestory, encroaching to a certain degree upon the dome. This, however, is not pendentive. It is covered externally by a roof. It has undergone much modernisation, but retains its general form and a good deal of its ancient decorations, which show it to have been treated much as St. Sophia, with which it was contemporary. The church is the more interesting from having been the type followed three centuries later by Charlemagne in his famous church at Aix-la-Chapelle (Fig. 433). The manner in which the dome was introduced and adopted in Italy during these ages, was so diverse in its results as to cause it to be very perplexing to chronicle it in any clear consecutive order. There were, in fact, two distinct influences, both occasionally leading to its adoption. [Illustration: Fig. 433. Plan and Section,--Church at Aix-la-Chapelle.] At Rome, and in places under Roman influence, such examples as the Pantheon could not fail to have their effect on the subsequent architecture, and we accordingly find there numerous scions of this primeval family, while, as we have just seen, the purely Byzantine form was simultaneously introduced by way of Ravenna, and later on was planted at Venice.