13. Our Saviour predicting the denial of Peter. 14. The denial of Peter. 15. Our Saviour before Pilate. 16. St.Peter taken to prison. These last six subjects are only represented on tombs.[216] The class of paintings shown as _Liturgical_ are less definite than these. In the Catacombs of Calixtus several obscure paintings are shown (in cubicula anterior to the middle of the third century), which are said to have reference to the sacrament of baptism. Pictures of the paralytic carrying his bed are identified by some Roman Catholic authorities with the sacrament of penance. (!) Bosio believed that in the Catacomb of Sta. Priscilla he had found paintings which illustrated the sacrament of ordination. Representations undoubtedly exist which illustrate the _agape_ or love-feast of the primitive Church. On the opposite side of the Via Appia from St. Calixtus (generally entered from the road leading to S. Urbano) is the _Catacomb of St. Pretextatus_, interesting as being the known burial-place of several martyrs. A large crypt was discovered here in 1857, built with solid masonry and lined with Greek marble. "The workmanship points to early date, and specimens of pagan architecture in the same neighbourhood enable us to fix the middle of the latter half of the second century (A.D. 175) as a very probable date for its erection. The Acts of the Saints explain to us why it was built with bricks, and not hewn out of the rock--viz. because the Christian who made it (Sta. Marmenia) had caused it to be excavated immediately below her own house; and now that we see it, we understand the precise meaning of the words used by the itineraries describing it--viz. 'a large cavern, most firmly built.' The vault of the chapel is most elaborately painted, in a style by no means inferior to the best classical productions of the age. It is divided into four bands of wreaths, one of roses, another of corn-sheaves, a third of vine-leaves and grapes (and in all these, birds are introduced visiting their young in nests), and the last or highest, of leaves of laurel or the bay-tree. Of course these severally represent the seasons of spring, summer, autumn, and winter. The last is a well-known figure or symbol of death; and probably the laurel, as the token of victory, was intended to represent the new and Christian idea of the everlasting reward of a blessed immortality. Below these bands is another border, more indistinct, in which reapers are gathering in the corn; and at the back of the arch is a rural scene, of which the central figure is the Good Shepherd carrying a sheep upon his shoulders. This, however, has been destroyed by graves pierced through the wall and the rock behind it, from the eager desire to bury the dead of a later generation as near as possible to the tombs of the martyrs.