The image of the Good Shepherd is the most common of the symbolic representations of Christ found in early Christian art in the Catacombs of Rome, before Christian imagery could be made explicit. The form of the image showing a young man carrying a lamb round his neck was directly borrowed from the much older pagan kriophoros (see below) and in the case of portable statuettes like the most famous one now in the Pio Cristiano Museum, Vatican City (right), it is impossible to say whether the image was originally created with the intention of having a Christian significance. The image continued to be used in the centuries after Christianity was legalized in 313. Initially it was probably not understood as a portrait of Jesus, but a symbol like others used in Early Christian art, and in some cases may also have represented the Shepherd of Hermas, a popular Christian literary work of the 2nd century. However, by about the 5th century, the figure more often took on the appearance of the conventional depiction of Christ, as it had developed by this time, and was given a halo and rich robes, as on the apse mosaic in the church of Santi Cosma e Damiano in Rome, or at Ravenna (right). Images of the Good Shepherd often include a sheep on his shoulders, as in the Lukan version of the Parable of the Lost Sheep.