It is easy to discriminate in early Christian art between the two apostles so highly honoured at Rome[559] by the strongly marked 337 conventional types to which their portraits almost invariably conform. St. Paul is characterized by the nobler form of face, a high, bold forehead, aquiline Jewish nose, dark hair and eyes, a flowing and pointed beard, and a refined and thoughtful expression of countenance as became one brought up at the feet of Gamaliel and instructed in all the wisdom of Greek philosopher and Hebrew sage. The Galilæan fisherman is represented with strongly-knit frame, broad rustic features, short gray hair, a thick and closely curling beard, generally of silvery white, and an expression of much force and energy of character.[560] It is probable that these types were derived from authentic tradition if not from actual portraits.[561] Eusebius, Augustine, and others of the Fathers, claim to have seen representations of these apostles preserved in painting; and the 338 reputed portraits alleged to have been sent by Pope Sylvester to the Emperor Constantine are annually exhibited at St. Peter’s for the veneration of the faithful.[562] Nowhere in the Catacombs do we find the least support for the notion that St. Peter is in any sense the founder of the church in Rome, much less the rock on which the church universal is built. That honour is assigned in early Christian art, as it is by the apostle himself, to Jesus Christ, the “chief corner-stone, elect, precious.”[563] [Illustration: Fig. 105.--Painted Chamber in the Catacomb of St. 339 Agnes.[564]] These biblical pictures, we may here remark, are not grouped indiscriminately, but are often arranged in a regular order having reference to their doctrinal signification. The walls and ceilings of the _cubicula_ are frequently divided into compartments of geometrical design, as shown in the preceding engraving of a chamber 340 in the Catacomb of St. Agnes. See also Figs. 82 and 89. Sometimes the paintings of a chamber are as closely related as the parts of a chapter in systematic theology. Thus on account of their common reference, as he conceives, to the sacraments of baptism and the eucharist, De Rossi designates as liturgical paintings certain pictures in the Catacomb of Callixtus.[565] An allegorizing spirit, however, will often discover a meaning in a fresco or relief altogether unthought of by the original artist. Thus Dr. Northcote interprets as personifications of the church or of the Virgin Mary, certain praying figures nowise differing from the ordinary _oranti_.