The above three edifices at Ravenna present fully developed examples of the three chief buildings required in connection with the church services up to the ninth century, viz., the church, the baptistery, and the mausoleum. As we proceed we shall meet with proofs that the same classes of edifices were in use and were carried out in a similar manner in other parts of the Western Empire. The circular or octagonal baptistery is of frequent occurrence in Southern Gaul. Examples of circular churches are also not awanting, but there is every ground for believing that the basilican form of church, like that of St Apollinare, was the plan most generally adopted in Western Europe. At Ravenna, an early circular tower or campanile, generally similar to the square ones at Rome and elsewhere, still exists. This is a feature the origin of which has not yet been accurately determined. The prevailing opinion, however, now is that these towers were at first erected as places of observation and defence, being in that respect somewhat similar in their conception to the round towers of Ireland. As in San Vitale, one form of a Roman octagonal-domed building is followed, so at San Lorenzo in Milan another design of a somewhat similar character is carried out, showing that the basilican form, although general, was not universal. In consequence of the destruction caused by the invasions of the Barbarians, by fire or otherwise, very few edifices now exist in Western Europe of the time between Justinian and Charlemagne. During all that time of disaster in the West, the Eastern Empire still maintained itself in splendour, and gave encouragement to architecture and the fine arts. From an early time the Byzantine architects showed a preference for the dome over the intersecting vault, and it is possible to follow in the still existing edifices, the mode in which the domical form of roof was gradually worked out, until in the great church of Sta. Sophia, erected under Justinian, in the sixth century, the largest and noblest building of the style was successfully completed. In the details of the style of the Lower Empire, as practised in the East, there is considerable evidence of Greek taste. The sharp thistle-like sculpture of the foliage is designed in a manner not unlike that of the Corinthian capitals of the Choragic Monument of Lysicrates at Athens. The Byzantines also excelled in flat and delicate carving, such as that generally executed in ivory or fine wood, and in ornamental metal work and jewellery. When the West began to revive, this Byzantine art naturally produced some influence on it. A very remarkable example of this occurs in the church of St Mark’s at Venice, erected about A.D. 950, which in every feature--in plan, in distribution of parts, in the use of the dome, and in its mosaic decorations,--is a distinct importation from Constantinople.