Sarcophagus of Valentinian III
Mausoleum of Galla Placidia, Ravenna, Italy
A label in the mausoleum gives the date as early 6th century and says the decedent is either Valentinian III or his uncle Honorius. But Valentinian died in 455 and Honorius in 423.
In the center panel a lamb and cross stand on a small hill, symbolizing the sacrifice of Christ, the "lamb of God," on the hill of Calvary. The birds on the crossbar bar represent the Resurrection and are derived from 4th-century images of the Crucifixion (example). New to the 5th century, as far as I know, are the lamb looking to the cross and the four rivers that flow from the base of the hill. The lamb's looking to the cross may represent a claim for the decedent's faith in Christ. The rivers most likely relate to the four rivers that rise from Paradise in Genesis 2:10, which Isidore of Seville interpreted as "the eternal flow of joy" (Glossa Ordinaria, I, 71). They thus represent the salvation that Christ earned for the faithful through the sacrifice of the Cross.
The four rivers also appear with the birds and another symbol of the crucified Christ on a sarcophagus in Sant'Apollinare in Classe.
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Photographed at the site by Richard Stracke, shared under Attribution-NonCommercial-ShareAlike license.