The 6th-century apse mosaic contains an interestingly symbolic depiction of the Transfiguration of Christ (Mt 17:1-9). Christ is represented by a golden cross on a starry blue background (99 stars to be exact), while the three apostles who were present at the Transfiguration - Peter, James and John - are represented by lambs. The large cross is decorated with mosaic gems and a bust of Christ in the center. It has a Latin inscription at its base reading SALVS MVNDI, "Salvation of the World" and a Greek inscription at the top: IXΘYC. This means "fish" in Greek and is also an acronym of the names of Christ: Jesus Christ Son of God Savior." The Greek letters Alpha and Omega are at the ends of the cross-arms.