The circle did not constitute a new form for worship, of course. Pre-Socratic philosophers had symbolized God as an "infinite sphere (31)." Bramante, an important Renaissance architect, was fascinated by the idea that the circle had no beginning or ending: "Such form," he said, "demonstrates the unity, the infinite essence, the uniformity and justice of God (32)."
Figure 14: Pantheon, Rome, Italy.
In fact, in all eras, the circle has been indicative of unity. The circle was even used in the Roman Pantheon, which predates Christianity and is dedicated to all the gods. It was reconstructed by Hadrian between 118 and 128 A.D. Its interior is composed of two very simple geometric shapes, a cylinder below and a dome above, both having the same diameter and height. The controlling axis of the building runs through the middle of the structure, thereby creating a vertical line from the center of the floor to the middle of the oculus, or circular opening (see Fig. 14) (33). The domed rotunda preceded by a pedimental porch that characterizes the Pantheon has often served as a model for Christian and non-Christian houses of worship. Indeed, at a later date the Pantheon itself was converted to a Place of Christian worship.
The circle as it related to the Christian churches can be traced back to Emperor Constantine's most important church in the east, the Church of the Holy Sepulchre in Jerusalem. The Anastasis Rotunda radiates from the tomb of Christ (see Fig. 15).
Figure 15: Anastasis Rotunda, Jerusalem.
Early Christian tombs and mausoleums also used the circular form. Among the most important of these was the Mausoleum of St. Constantia, a Roman memorial built by the Emperor Constantine for his daughter. The building is a circular, domed structure with arched windows in its drum. Around the drum is a continuous circular passage with a barrel vault. This mausoleum represents a critical link between the Roman period and the Byzantine period when the arcade, the circular passage, and the dome were often brought together to create a single, centralized structure (see Fig. 16) (34). San Lorenzo, in Milan (begun in 378) was equally important because of its use of a circle inscribed within a square (35). This circle within a square served as a prototype for many of the later Renaissance churches. St. Vitale, in Ravenna, Italy (begun in 540), though more complex, also emulated the earlier design of St. Constantia (see Fig. 17) (36).
Figure 16: Mausoleum of St. Constantia, Rome, Italy.
Shortly after Christianity became the official religion of the Roman empire, the imperial center shifted from Rome to Constantinople, where the Byzantine style reached its apogee in the great church of Hagia Sophia. Here the dassical style, with columns supporting the entablature, or framework, and a roof, was fused with the oriental tradition of a square plan surmounted by a dome. The series of com- partments growing out from the central area of the dome made possible a variety of semi-domes (37). Churches with centrally-focused worship spaces became standard in the east.
During the Byzantine era, the use of circular forms in ecclesiastical structures gradually waned in the west, where the processional plan remained more important. It took the emergence of the Renaissance and of the Baroque and the Mannerist periods to reintroduce centralized worship space. Indeed, the earliest iterations of St. Peter's by Bramante and Michelangelo had central foci. Bramante's San Pietro in Montorio in Rome and the Church of Santa Maria della Consolazione in Todi (begun in 1508) are two surviving examples of this centralized type (see Fig. 18 and 19).
Figure 17: San Vitale, Ravenna, Italy.
Figure 18: San Pietro in Montorio, Rome, Italy.
Figure 19: Santa Maria della Consolazione, Todi, Italy.
