Another very interesting plan occurs in the =Cathedral at Borah=. It presents a circle inscribed in a square, in the angles of which are apsidal recesses projecting from the circle. Moreover, from the east side of the square project three short rectangles, terminating in apses, which suggest the prolongation of the nave and aisles that have been interrupted by the circle. Nothing but the foundations of this church remain. Meanwhile, the =Church of S. George= at =Esrah= shows a similar plan and is surmounted by a high elliptical dome. It is conjectured that these two churches were the prototypes of =S. Sergius, Constantinople=, and =S. Vitale= at =Ravenna=, which will be discussed later, and of many corresponding churches of Byzantine architecture. =Ravenna.=--In the development of early Christian architecture a very interesting part was played by Ravenna. For this city, situated on the Adriatic (though the sea has since receded to a distance of six miles), was the chief port by which the trade of Constantinople or Byzantium entered Italy. Accordingly some of the tombs and churches present a fusion of Byzantine and Syrian influences with Roman. The change from the basilican type is especially marked in the character of the plan and by the adoption of domes. Thus the =Baptistry of Ravenna= is an octagonal structure, surmounted by a dome of hollow tiles. The =Tomb of Galla Placidia= is cruciform in plan with a lantern raised over the crossing or intersection of the arms of the cross. The lantern is pierced with four windows and surmounted by a dome, supported on pendentives--a method of construction, peculiarly Byzantine, which will be considered presently. When Theodoric the Great, King of the Ostro-Goths and ruler of Northern Italy, selected Ravenna as his capital, he built the =Church of S. Apollinare Nuovo=, importing twenty-four marble columns from Constantinople and employing Byzantine artists and artisans. The plan is basilican, though the atrium and apse have been removed by subsequent alterations, but the interior is richly embellished with Byzantine mosaics. The latter also adorn the larger basilican =Church of S. Apollinare-in-Classe=, so called from its being situated near the port. Its columns also are distinguished by the peculiarly Byzantine feature of the _impost block_, to be described later. After the death of Theodoric in 536 the Emperor Justinian, having through his general, Belisarius, routed the Goths from the country, made Ravenna the political capital of Italy, under the authority of an exarch. Then was built, probably as Court Church, the famous example of Byzantine influence, the =Church of S. Vitale=. We will return to this after a consideration of what is involved in the Byzantine style.