The mosaics in Santa Cecilia in Trasteveredate back to the reign of Pope Paschal I (r. 817-24), who built the church to house the remains of St Cecilia and her husband St Valerius.
Paschal I appears in the mosaic in the apse carrying a model of his church; his halo is square to show that he was still alive when the mosaic was made. Above his halo, perched on a branch of a palm tree, is a phoenix, a symbol of the Resurrection.
In the centre of the mosaic stands Christ. To the left stand St Paul, St Agatha and Paschal I, and to the right St Peter, St Valerian and St Cecilia. The two female saints wear crowns and are dressed as Byzantine princesses. Each sports a pair of red shoes, a sign of high status.
At the lower level, twelve lambs (representing the Apostles) emerge from the cities of Bethlehem and Jerusalem and converge on the Agnus Dei (Lamb of God).