Long before any churches were open to the public, the apostles “broke bread with, the faithful” in the guest chamber of private dwellings; their disciples followed their example in the subterranean cemeteries, termed Catacombs, where the early Christians used to assemble to celebrate the Lord’s Supper (Fig. 175). This sacrament, the primitive form of which is unknown to us, was not termed a _mass_ (_missa_) till the middle of the fourth century. “It was on a Sunday,” says St. Ambrose, who was the originator of the Ambrosian rite, “that I first held a mass.” The name of mass, about the meaning and origin of which the most learned Christian archæologists are by no means agreed, appears to have been derived from a Hebrew word denoting an offering or sacrifice; or perhaps rather from the Latin _missa_, from _mittere_, to send away, or to take leave of. Apostolical discipline required that the sacrament should be preceded by a discourse, and that before it was celebrated the catechumens, those who had not yet been baptized, should leave the sanctuary. “After the sermon,” says St. Augustine, “the catechumens are sent out” (_fit missa_). [Illustration: Fig. 176.--Miraculous Mass of St. Gregory the Great (Sixth Century), depicting the real presence of Jesus Christ in the eucharist.--Miniature from a Missal of the Fifteenth Century, in the Collection of M. Ambr. Firmin-Didot.] There was, however, a mass for the catechumens which comprised the introductory prayers, lessons from the Old and New Testaments, and the bishop’s homily. The true mass, celebrated for the faithful alone, was specially called the eucharist. “Those are masses,” says St. Cesarius of Arles, “when the body and blood of Christ are offered up in sacrifice” (Fig. 176). At first, mass was celebrated once a week, and always on the Sunday. In the second century, the sacrament or eucharistic offering took place three times a week, on Sunday, on Wednesday, and on Friday. In the following century, the Eastern Church decreed that it should also be celebrated on Saturday. In the West, mass was held only on Sundays, unless in exceptional cases; while in the days of St. Augustine, in the dioceses of Africa, Spain, and Constantinople, it was celebrated generally every day. It was not till the sixth century that it became usual in the Latin Church to celebrate mass every day.