Apse

APSE (APSIS): The semicircular or semioctagonal enclosure with which the choir of the older Christian churches generally terminates. The ground-plan of this enclosure is an arc, on the chord of which the altar is raised, while the bishop’s throne is placed in the center, against the wall, with rows of benches for the clergy on both sides, sometimes one row above the other (apsides gradatæ). In the Roman basilica, or hall of justice, which in numerous cases was actually turned into a Christian church with very slight modifications, while its ground-plan formed the starting-point for all Christian church architecture, the exterior form of the building was perfectly rectangular, and the apse, with its seats for the magistrate and the officers of the court, was formed internally.

There are still churches extant on this plan, and they are the oldest; such as the Sta. Croce in Gerusalemme in Rome, and several others in Africa and Asia Minor, all of the third century. In churches of the fifth century, such as Sant’ Apollinare in Classe at Ravenna, etc., the apse has generally become visible also in the exterior form; and not only the choir, but also the aisles, terminate in apses. In St. Sophia in Constantinople, and in churches built after that model, the transepts are provided with apses; and, in some few cases in Germany, such as the Church of Reichenau on the Lake of Constance, the choir has apses at both ends. See Architecture, Ecclesiastical.