The Lamb of God and the Four Rivers of Paradise
Left: Sant'Apollinare in Classe, Ravenna Right: Archeological Museum, Split
On the right is a sarcophagus fragment in the Archeological Museum, Split, Croatia. The museum's guide pamphlet dates it as 5th century and explains that the lamb is standing on the source of the four rivers of Paradise (Genesis 2:10-14). Above its head a modified chi-rho symbol is incised in red, showing that the lamb represents Jesus Christ. The red letters on this fragment and on two others displayed to the left and right of this one list the names of the apostles, who are also represented as lambs. (See this page for all three fragments.)
On the left is a similar representation of the lamb, on a sarcophagus at Sant'Apollinare in Classe, Ravenna. Its date would be somewhere from the 5th to the 8th century. Again we see the lamb standing on a height from which four rivers flow. The chi-rho symbol in this case is inscribed on the halo. (Follow this link for the front and right sides of the sarcophagus.)
This particular iconographical type is even seen as late as this mid-twentieth century window in an English church.
View in full resolution the image on the right and the image on the left.
Read more about the Lamb of God symbol.
Photographed at the sites by Richard Stracke, shared under Attribution-NonCommercial-ShareAlike license.