We pass on to another of the Biblical stories mentioned by several of the Fathers as typical of baptism; and we will select as our specimen of it a painting that was executed about the very time that Tertullian was writing his treatise on that sacrament. It is to be seen more than once on the walls of a series of chambers which open out of a gallery in the Catacomb of San Callisto, not far from the papal crypt. The first figure that greets us from the wall on the left-hand side as we enter these chambers is Moses striking the rock and the water gushing forth. Are we to look upon this as a mere historic souvenir of the Jewish legislator, or are we to see in it a reference to Christian baptism? The artist in the present instance does not allow us to doubt. Side by side with it he has painted a fisherman, and we need not be reminded who it was that compared the work of the Christian apostle to that of fishermen; and immediately he adds, with still greater plainness of speech, a youth standing in the water, whilst a man pours water over his head. Finally, he fills the very little space that remains on the wall with the picture of a paralytic carrying his bed, and it would be easy to show that the Fathers recognized in the pool of Bethsaida, to which place this history belongs, a type of the healing waters of baptism. Was it possible for the Christian artist to set forth the sacrament more unequivocally? There is no legend to interpret the painting, but surely this is not needed. The mystery is veiled, indeed, from all who were uninstructed; but it was perfectly intelligible to all the baptized; it was veiled under types and symbols taken partly from the Old Law and partly from common life. We need hardly say that this same figure of Moses striking the rock occurs in scores of other places throughout the Catacombs; but we have selected this particular specimen, both because it appears with a more copious _entourage_ of other symbols determining its sense beyond all dispute, and also because it is here brought, as we shall presently see, into immediate proximity with the other sacrament, to which it is a necessary gate of introduction—the Sacrament of the Holy Eucharist. But before we pass on to examine the symbols of the Holy Eucharist, let us first inquire whether there is anything further about baptism to be gleaned from the Catacombs—not now from their paintings, but from their inscriptions.