Confessio was originally the place where a saint or martyr who had "witnessed a good confession" for Christ was buried, and hence the altar raised over his grave, and subsequently the chapel erected on the hallowed spot. From its subterranean position such an altar was known as descensus. Of these underground "confessiones" we have many examples in Rome, above all, in the Basilica of St. Peter's. Not unfrequently they were merely imitative, as in the crypts of early churches in England. The term was also used for the altar in the upper church, placed immediately above that built over the martyr's grave, sometimes covered with silver plates, and its canopy.
This memorial to a saint was a tomb beneath an altar containing a window, called the jugulum, or cataract, through which the pilgrim let down a cloth (called the pall, brandeum, sudary, or sanctuary) to touch the body below. It was surrounded by a screen of perforated marble, or a rail of bronze, and was often closed in with pillars, covered with metal plates, and illuminated by lights and candelabra. The theory was, that every church was erected over a catacomb: and where it was impossible to have a real confessio, relics were enclosed within an altar, which was erected on an elevated platform, and called the confessio. The true confessio was the germ of the crypt; in Old St. Peter's it formed a subterranean Chapel of St. Peter. At the beginning of the 13th century the steps to it were removed. and the entrance closed. The altar built over the actual grave was the lower confessio; the upper confessio was the larger altar of marble erected above it, in the church itself, as at Santa Prisca, San Silvestro, San Martino, and San Lorenzo ir Rome.
Concilia martyrum is applied to the burial-places of the martyrs in the catacombs. Jerome uses a similar expression, in speaking of the graves the young Nepotian had been in the habit of decorating with flowers.
Memoriae martyrum is a term of constant occurrence in early Christian writings for the memorial chapel of a saint or martyr, also called cella. The church of St. Euphemia, where she lay buried, in which the Council of Chalcedon was held, is styled in the acts of that council martyium; and also that erected by Constantine over our Lord's sepulchre on Calvary. The word tropaea is used for the tombs of Peter and Paul in the Roman cemeteries. SEE CELLA MEMORIE.