is a term used in early Christian architecture in two senses.
1. We find it employed to denote what we should now call the side chapels of the nave of a church. The first instance of its use in this sense is in the writings of Paulinus of Nola, who describes the church erected at Nola, and particularizes these side chapels, which were evidently novel features in church arrangement. There were four on each side of the nave, beyond the side aisles, with two verses. inscribed over the entrances. Their object was to furnish places of retirement for those who desired to pray or meditate on the word or God, and for the sepulchral memorials of the departed. They differed from the side chapels of later ages in containing no altars, as originally there was but one altar in a church. Paulinus also speaks of these chapels under the name of cellae or celluic, e.g., when speaking of a thief who had concealed himself in one of them all night. Perhaps the earliest existing example in Rome of such a chapel attached to the body of a church is that of St. Zeno in the Church of Santa Prassede, built by pope Paschal I about A.D. 817.
2. The word cubiculum is likewise employed to designate the family grave chambers in the subterranean cemeteries at Rome. In addition to the ordinary places of interment in the ambulacra, the catacombs contain an immense number of sepulchral chambers or cubicula, each enshrining a larger or smaller number of dead, as well in table tombs and arcosolian — as in loculi pierced in the walls. These were originally family burial-places, excavated and embellished at the expense of the friends of the departed, and from the date of their first construction served for the celebration of the eucharistic feast and agape, on the occasion of the funeral, and its successive anniversaries. In times of persecution they may have supplied places of religious; assembly where the faithful might gather in security for the celebration of the holy mysteries, at the graves of the departed martyrs and others whose fate they might be soon called to share by sealing their testimony with their blood. The name cubiculumi is of exclusively Christian use as applied to places of interment. From inscriptions in which the term occurs, March infers "that in the 14th century the persons named caused that their own cubicula should be excavated at their own expense. Each cubiculum was of sufficient dimensions to serve for several generations of the respective families. If it proved insufficient loculi were added at a greater or less distance from the cubiculum." Sometimes we find the arch of an arcosolium of the 1st century cat'through and used as a door or entrance to a second cubiculum excavated in its rear, the original sarcophagus being removed and carried to the back of the chapel that- other bodies might be placed near it. The number of these sepulchral chambers is almost beyond computation. March reckons more than sixty in the eighth part of the. catacomb of St. Agnes. In that of St. Callixtus they amount to some hundreds. They are equally frequent in the other cemeteries. Their form is very varied. In the catacomb of St. Callixtus, with very few exceptions, they are rectangular, and that appears to have been the earlier shape. But there are examples of many other forms, triangular, pentagonal, hexagonal, octagonal, circular, and semicircular. The roof is sometimes a barrel vault, sometimes a coved ceiling, nearly flat; in one instance, it expands into a lofty dome, lighted by a luminare. Both the roof, the vaults, and the recesses of the. arcosolia are generally coated with stucco, and richly decorated with religious paintings. In the later restorations the walls are often veneered with plates of costly marble. SEE PLATONIA. In a very large number of examples the Good Shepherd occupies the centre of the ceiling, the surrounding lunettes containing Adam and Eve after the Fall, The History of Jonah, The Sacrifice of Abraham, Moses Striking the Rock, The Three Children in the Furnace, The Visit of the Wise Men to Christ, The Raising of Lazarus, The Healing of the Blind Man, The Paralytic Carrying his Bed, The Miracle of the Loaves, and other scenes from the limited cycle of Scriptural subjects to which early Christian art confined itself, treated with a wearisome uniformity; embellished with palm branches, vines laden with grapes, the dove, the peacock, and other familiar Christian symbols. The walls of the chamber were also similarly decorated. SEE FRESCOES. The vault is in some cases supported by columns, either cut: out of the tufa, or formed of brick coated with stucco. Light and air were not unfrequently admitted: by means of a shaft communicating with the surface of the ground, called luminare. A chamber so lighted was known as a cubiculum clarum. These cubicula were very frequently double, one on either side of the gallery, and, as we have just noticed, in some instances a luminare was sunk in the centre so as to give light to both. The cubicuia, generally speaking, are of small dimensions, and are incapable of containing more than a very limited number of worshippers. But there are also found halls and chambers of much larger proportions, which have been considered by the chief Roman Catholic authorities on the subject to have been constructed for the purpose of religious assemblies. These are distinguished by Marchi, by an arbitrary nomenclature, into cryptae, for the smaller, and ecclesiae, for the larger, excavations. SEE CATACOMBS.