The semicircular or polygonal termination to the choir or aisles of a church. A similar termination is sometimes given to transepts and nave. The term in ecclesiastical architecture generally denotes that part of the church where the clergy are seated or the altar placed. It was so called from being usually domed or vaulted, and was so used by the Greeks and Romans. The term is sometimes applied to a canopy over an altar; a dome; the arched roof of a room; the bishop's seat in old churches; a reliquary; a recess, semicircular in plan, covered over with a vault in the shape of a semi-dome or any other description of roof. The apse is always solid below though generally broken by windows above. The chevet is an apse, always enclosed by an open screen of columns on the ground floor, and opening into an aisle, which again opens into three or more apsidal chapels. Sometimes the apse is a simple semicircle; out of this, in some large churches, a smaller semicircle springs, as Becket's crown at Canterbury, and as in the churches at Sens, Langres, and many others in Europe. Sometimes the choir finishes with three apses-one to the central aisle and one to each side aisle, as at Autun. Sometimes the plan is a semicircle, each bay of which has a projecting semicircular apse, forming a sort of cluster of apses, as at Beauvais, Troyes, Tours, etc. The choir of late date at Le Mans is encircled by no less than thirteen apses, the centre one being twice the depth of the others, and forming the Lady Chapel. Large circular and polygonal apses generally have radiating chapels within, as at Westminster Abbey. The term apse was first used in reference to a Roman basilica, of which it was a characteristic feature. There was an apse in the temple of Mars Ultor. It is now completely decayed, but in the time of Sabacco and Palladio there seem to have been sufficient remains to justify an attempt at restoration. It is nearly square in plan (112 feet by 120). The cella here is a much more important part than is usual in Greek temples, and terminates in an apse, which afterwards became characteristic of all places of worship. In Trajan's basilica at one end was a great semicircular apse, the back part of which was raised, being approached by a semicircular range of steps. In the centre of this platform was the raised seat of the quæster or other magistrate who presided. On each side, upon the steps, were places for the assessors or others engaged in the business being transacted. In front of the apse was placed an altar, where sacrifice was performed before commencing any important public business.

In the basilica, when used as a place of Christian worship, dating from the fourth century, the whole congregation of the faithful could meet and participate in the ceremonies and devotions. The bishop took the place occupied of old by the prætor or quæster; the presbyters, the places of the assessors. Very little change was needed to erect a Christian altar on the spot in front of the apse, where the heathen had poured out their libations at the commencement and conclusion of all important business. The basilica of the heathen became the ecclesia, or place of assembly, of the early Christian community. In the church of Ibrihm, in Nubia, there is the peculiarity of an internal apse, which became general in Eastern, but less frequent in Western, churches, though sufficiently so to make its introduction at this early period worthy of notice. Another example to make this early form intelligible is that of the church of St. Reparatus, near Orléansville in Algeria, the ancient Castellum Tingitanum. According to an inscription still existing, it was erected in 252; but the second apse seems to have been added about the year 403, to contain the grave of the saint. As it now stands, it is a double-apsed basilica, 80 feet long by 52 broad, divided into five aisles and exhibiting on a miniature scale all the peculiarities of plan which we once fancied were not adopted until some centuries later. In this instance both apses are internal, so that the side aisles are longer than the central one, apparently no portion of them having been cut off for calcidica or vestries, as was very often done in that age. At Parenzo in Istria there is a basilica built in the year 542, with three aisles and an apse at the end of each. The church at Torcello, near Venice, presents one of the most extensive and best preserved examples of the fittings of the apse, and gives a better idea of the mode in which the apses of churches were originally arranged than anything to be found in any other church, either of the same age or earlier. The apse in the chapel of St. Quinide, probably of the ninth or tenth century, is the most singular as well as the most ancient part of the church, and is formed in a manner of which no other example seems to be known. Externally, it is two sides of a square; internally, a semicircle; at each angle of the exterior and on each face is a pilaster fairly imitated from the Corinthian order, and supporting an entablature that might very well mislead a Northern antiquary to mistake it for a pagan temple. The plan of the church at Planes deserves to be quoted, if not for its merit, at least for its singularity; it is a triangle with an apse attached to each side, and supporting a circular part terminating in a plain roof. As a constructive puzzle it is curious, but it is doubtful how far any utility was subserved by such a freak. The church of Ste-Croix at Mont Majour near Arles is a triapsidal church, supposed to be the only one of its kind. Built as a sepulchral chapel, it is a singularly gloomy but appropriate erection. In the Byzantine style the apse was retained, as in St. Sophia at Constantinople, in the old Byzantine churches at Ravenna, and in several churches on the Rhine.

The apse is almost universally adopted in Germany, and is very common in France and Italy. In different parts of England there are many churches with semicircular apses at the east end, chiefly in the Norman style, and some in which this form has evidently been altered at a subsequent period. In several cases the crypts beneath have retained the form when the superstructure has been altered. The apse is virtually a continental feature and contrasts with the square termination of English Gothic work. The traditional semicircular apse, greatly enlarged and, in the perfected style, changed to a polygonal plan, is the most characteristic eastern termination of the larger French churches. The low Romanesque apse, covered with the primitive semi-dome and enclosed with its simple wall, presented no constructive difficulties and produced no imposing effect. But the soaring French chevet, with its many-celled vault, its arcaded stories, its circling aisles, and its radial chapels, taxed inventive powers to the utmost and entranced the eye of the beholder. The apse of St. Germain-des-Prés (second quarter of the twelfth century) may reasonably be regarded as the first great Gothic apse ever constructed. Norwich cathedral is perhaps the finest example of the round apse in England. The cathedral of Durham, of which the nave and choir were finished much as they are now seen about the beginning of the twelfth century, had originally an apse; but on account of a defect in the masonry this was taken down and the present magnificent chapel of the Nine Altars substituted in the thirteenth century. The apsidal form is occasionally met with in England, as at Lichfield and Westminster. There is an apse in each arm of the transept in the churches at Melbourne, Gloucester, Ramsay, Chichester, Chester, Norwich, Lindisfarne, Christ Church in Hants, Tewkesbury, Castle Acre, Evesham. If the transept was long, there would sometimes be two apses on each arm, as at Cluny, Canterbury, St. Augustine's, and St. Albans.

FERGUSSON, A History of Architecture in all Countries (London 1893), GWILT, Encyclopedia of Architecture (London 1881); FLETCHER, A History of Architecture (London, New York, 1896), WEALE, Dict. of Terms in Rudimentary Series (London, 1859-93); MOORE, Development and Character of Gothic Architecture (London, New York, 1899); LONGFELLOW (ed.). A Cyclopedia of Works of Architecture in Italy, Greece and the Levant (New York, 1895).

THOMAS H. POOLE