Shortly after Emperor Constantine established Christianity as the official religion of the Roman Empire, Christians began to believe that places rather than individuals were associated with God's presence and so they used the word "church" to designate both a community of people and places where they met.(1)

In the early days of the Christian Church, the Roman basilica exerted a powerful influence on church form. Romans used the term "basilica" to identify buildings used for public assembly, the exchange of goods, or the administration of justice. After the Christians gained imperial sanction, they adopted the basilican form for religious purposes because, as one church historian says, "They were delighted to Practice their religion in spaces that involved the power of the law."(2) An outstanding example of such a building is the Basilica of Constantine, begun by Maxentius about 306 and completed by Constantine about 313. The basilica is impressive because of its mass, size, and innovative technology. Measuring 215 by 300 feet, it had a high central space, or nave, rising 114 feet. Light flooded the interior through the ends of the curved ceiling, which were left open. Predating the Gothic buttress system by seven hundred years, buttresses, or piers, reinforced the ceiling vault (see Fig. 1).

More typical earlier basilicas, such as the Basilica Ulpia in Rome, constructed about 112, had entrances on their long sides and semi-circular forms called apses on each of their short ends. In halls of justice the apse, which terminated the visual axis, could be placed at the end of either the long or short axes. But when older structures were converted into Christian places of worship, or when new structures were erected, the apse was always placed at the end of the long axis to reinforce the idea that the shrine was the focus for the whole design and the place of the central mystery of the Christian faith.(3) The longer nave created a sense of spatial procession by establishing a focal point to reinforce the directional signals given by the primary axis.

Because the basilica form served the liturgy well and was relatively simple to build, it soon became the basic plan for many churches. The early basilican churches generally consisted of several basic elements: the narthex, or vestibule; the nave, or main body of the church; the low side aisles; and the transverse aisle, or transept, placed between the nave and the apse and projecting beyond the walls of the nave and the aisles. All of these features can be identified in Old St. Peter's in Rome, dedicated about 330 (see Fig. 2). Because it served as a model for so many churches, it is considered by many to be the most important design in the history of church architecture.(4)

The nave of the old St. Peter's might be compared to an elongated shoe box placed on its side: it was long, narrow, and high. Three bands of elements made up of columns formed the two longer sides of the space. At the lowest level, the load of the upper building mass was transferred to a series of columns that divided the side aisles from the nave. Above this was a level of masonry surmounted by a series of windows called a clerestory, which admitted light. The basic elongated form of the nave directed attention forward, toward the altar.(5)

Parallel to the nave and reinforcing the movement toward the altar were the aisles. These were considerably narrower and lower than the nave. Projected from the aisles at right angles were two basic transept forms. In one, the colonnades of the nave ended just before the transept began. This created a continuous transept and the short axis remained undivided. This second form created a "swelling in the nave" called a cross transept.(6) In such a form the colonnades turned at right angles and entered into the wings.

The combination of the proscenium or triumphal arch and the apse was a Christian feature added to the Roman basilica. The arch reinforced the direction implied by the nave and the aisles; in this sense it became a symbolic gateway to the altar and bishop's seat. The semi-circular form of the apse, aligned with the main axis, created a final point for all forward movement and framed the altar.(7)

In the early Christian church the procession was terminated by the bishop's seat. This was important because the bishop represented Christ to the congregation; he was the congregation's shepherd. He dressed in the sacristy as the congregation prepared to receive him; he followed them in the procession and passed through them on his way to the altar. Continuing to his place at the extreme focal point of the apse, he then faced the altar and people. Above him, iconographers frequently displayed the Christ of the second coming. Mass at the altar represented the joy and nourishment of Christian life in this world and the promise of future life with Christ in eternity. The shepherd instructed his people, facing them from the throne; he then came before the altar at the offertory and acted as a mediator with Christ during the mass.(8)