Early Christian art found in the catacombs in Rome shows Jesus carrying a lamb on his shoulders.The image of the Good Shepherd, who lays down his life for his sheep, is found in the Gospel of John 10:11-18:
I am the good shepherd. A good shepherd lays down his life for the sheep. A hired man, who is not a shepherd and whose sheep are not his own, sees a wolf coming and leaves the sheep and runs away, and the wolf catches and scatters them. This is because he works for pay and has no concern for the sheep. I am the good shepherd, and I know mine and mine know me, just as the Father knows me and I know the Father; and I will lay down my life for the sheep.
I have other sheep that do not belong to this fold. These also I must lead, and they will hear my voice, and there will be one flock, one shepherd. This is why the Father loves me, because I lay down my life in order to take it up again. No one takes it from me, but I lay it down on my own. I have power to lay it down, and power to take it up again. This command I have received from my Father.
That image can be found in the Catacombs of Rome, at a time when it was illegal to create more explicitly Christian art. The art left behind by early Christians offers us a window into their faith. Painted on the walls of the St. Callisto catacomb in Rome sometime in the middle of the 3rd century is an image of Jesus carrying a sheep across his shoulders.
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And around the same time, or perhaps a century later, early Christians left another image of Christ as the Good Shepherd, in the Catacomb of Priscilla in Rome. Here, Jesus is portrayed with a lamb on his shoulders and two sheep at his sides, representing his flock.
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And in Domitilla’s catacomb we find this, perhaps the earliest existing image of the Good Shepherd, dating back to the 2nd century.
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While this image can be found in pagan cultures in which animals were offered as sacrifices to the gods, it takes on a Christian meaning inspired by the words of the New Testament.