Certain aspects of Christian architecture changed quickly and
dramatically between the Early Christian and Gothic periods, but the basic basilica plan remained throughout. Christian worship, being congregational, requires a hall, and the Roman basilica - a civic lawcourt - became the early model for both large and small churches. The basilica, processional in form, had a long axis running from a centered doorway to the altar at the other end of the building. They were generally shaped like a cross, either in the form of a Greek cross (with arms of equal length) or a Latin cross (with one longer arm, the nave).
One of the earliest examples of Christian architecture and an excellent example of the basilica plan was Old St. Peters in Rome. It was built by Emperor Constantine shortly after he legalized Christianity, around 333 C.E. Like many other pilgrimage churches, it was built over the grave of a saint.
…
