Bk. IX. Ch. IV. NEO-BYZANTINE STYLE. 453 now find it by Leo the Isaurian (a.d. 718-740). It differs in several essential jDarticulars from the old style, and contains the germ of mucli that we find frequently repeated. The change is not so great as might have taken place in two centuries of building activity, but it is considerable. In this church we find, apparently for the first time in a complete form, the new mode of introducing the light to the dome through a jDerpendicular drum, which afterwards became so universal that it serves to fix the age of a building in the East with almost as much certainty as the presence of a pointed arch does that of a building in the West. As this invention is so important, it may be well to recapitulate the steps by which it was arried at. The oldest mode of lighting a dome is practised in the Pantheon (Woodcut No. 191), by simply leaving out the central portion. Artistically and mechanically nothing could be better, but before the invention of glass it was intolerably inconvenient whenever much rain or snow fell. A change therefore was necessary, and it is found in the tomb or temple of Marcellus, built during the reign of Constan- tine on the Via Prenestina at Rome. It consists simply of boring four circular holes through the dome a little above its springing. The next step is seen at Thessalonica in the church of St. George (Wood- cut No. 878). There eight semi-circular lunettes are pierced in the dome, at its springing, and answer the purjjose very perfectly. The system culminated in Sta. Sophia, where forty windows introduce a flood of light without its ever falling on the eyes of the spectator. After this it seems to have been considered desirable not to break the liemisphere of the dome, but to place the windows in a perpendicular circular rim of masonry — called the drum — and to introduce the light always through that. • Externally there can be no doubt but that this was an improvement; it gave height and dignity to the dome in small churches, where, without this elevation, the feature would have been lost. Internally, however, the advantage is problematical : the separation of the dome from its pendentives destroyed the continuity of the roof, and introduced the stilted effect so objectionable in Renaissance domes. In the Neo-Byzantine churches the dome became practically a skylight on the roof, the drum increasing in height and the dome diminishing in dignity as the style progressed. As all the churches are small, the feature is unobjectionable; but in larger edifices it Avould have been found difficult to construct it, and the artistic result would hardly have been pleasing, even had this difficulty been got over. Be this as it may, its value as a chronometric land- mai-k is undoubted. As a rule it may generally be asserted that, in all Christian domes erected during the old Byzantine period, the light is introduced by openings in the dome itself. After that time, the light is as generally
