The important early surviving illustrations of the dome churches are the chapel built by Charlemagne, already mentioned, the church of St. Mark at Venice, the church of San Vitale at Ravenna, the church of St. Sophia at Constantinople, and possibly the “Dome of the Rock,” or Mosque of Omar, at Jerusalem. It was the theory of the English architect, Fergusson, that this building was a Christian church of the fourth century, built over the supposed site of the Holy Sepulcher. The present dome, the exterior decoration of porcelain tiles, and the inserted pointed-arch windows are Arab reconstructions. The Arian Baptistery at Ravenna (fifth century) and the Baptistery of St. John Lateran at Rome (fifth century) are smaller buildings of the same general type.
Among the buildings named and illustrated those are most obviously available as indications of the type which are most obviously of a radiating plan. The domed ceiling was naturally used for such a building and herein lies the distinction as compared with the long perspective view of the basilicas. It was from the great domed apartments of the Roman baths that this plan of construction was adopted and even their name was retained. They were called “baptisteries,” that is to say, baths ; and the title of baptistery, or bath, survived as applied to the churches copied from them.
The name and plan subsequently became distinctive in Italy for a building specially designed and used for baptisms, which were always by immersion in the early church. Each Italian city of the Middle Ages possessed one of these buildings which we must carefully distinguish from the baptistery churches. These were generally abandoned in Western Europe after the beginning of the Romanesque period.
By its grand dimensions and grand interior effect the church of St. Sophia at Constantinople surpasses all other buildings of its time and most of those which have followed it. It was built in the sixth century by the Emperor Justinian. The height of the main dome from the floor is one hundred and seventy-seven feet, its diameter is one hundred and six feet.
It is probable that the dome was more commonly employed in earlier Oriental buildings than the actual remains would visibly indicate, and this view has been recently much advocated by experts of distinction. According to this view the Roman use of the dome would go back to Mesopotamian originals, which continued its use in their earlier home down to and after the Byzantine period. There is no doubt that Byzantine architecture especially affected the dome, and that in Western Europe its use was continued by that influence. As visible reminder of the antique originals of the form we are confined to the Pantheon at Rome, which must rank with the church of St. Sophia, as one of the two finest dome constructions of the entire world. The merit of these buildings as compared with later ones which have used the dome, like St. Peter’s at Rome, St. Paul’s in London, or the Cathedral of Florence, is that the interior effect is immeasurably superior, because the domed apartment itself constitutes the whole interior. To place a dome above a portion of a cathedral, as done in the cases just mentioned, may or may not add to the exterior effect in adequate proportion to the expense and effort necessary in the cases named, but the dome is lost for an interior which is not distinctly planned for it. The Pisa Cathedral is by far the finest instance of a building using the dome in combination with the oblong cathedral plan, because its modest proportions do not antagonize the main plan.