The Catacomb of Callixtus was built along the Appian Way, probably by Pope Calixtus in the early third century. As Christianity became prominent, catacomb remains were moved to churches and catacombs fell into disuse.
"In the catacomb of Callixtus, dating from the middle of the third century, the Good Shepherd appears again with delicate modelling of form, face, and drapery. Shepherds were common enough as garden figures in pagan villas; they represented a romantic ideal of the bucolic way of life and the more solid merit of good husbandry and economy, but they could equally well be adapted to Christian symbolism. [John Beckwith, "Early Christian and Byzantine Art, Volume 1979." Yale University Press, 1979, p. 21.]