The mosaic in the apse of the church of Santi Cosma e Damiano was created during the reign of Pope Felix IV (r. 526-30).
In the centre of the mosaic stands Christ. He is dressed in a golden toga, which is embroidered with what looks like the letter iota, the tenth letter of the Greek alphabet, possibly a reference to the Ten Commandments. Christ is thus the Law and the Word made flesh.
Christ is flanked by St Peter and St Paul (patron saints of Rome), who are presenting St Cosmas and St Damian, two Arab physicians (reputedly twins), who were martyred towards the end of the 3rd century. On the far right is St Theodore and on the far left Pope St Felix IV, who holds a model of the church. The latter figure only dates back to the 1630s when this part of the mosaic was reworked.
Directly below Christ, at the bottom of the mosaic, the Agnus Dei (Lamb of God) stands on a mount, from which flow the four rivers of Paradise. The Agnus Dei is flanked by twelve sheep representing the twelve apostles. At either end of the row of sheep are, respectively, the cities of Bethlehem and Jerusalem.
The mosaic on the choir arch, which may be of a later date than the mosaic in the apse, is based on the first chapters of the Book of Revelation. In the centre sits the Lamb of God on a throne with a Cross above and the Scroll with the Seven Seals below. The Lamb is flanked by seven candlesticks and four angels. In the upper corners are the winged figure of St Matthew and the eagle of St John. In the lower corners are two up-stretched arms. The arms belong to two of the twenty-four elders of Revelation. They, and the other two symbols of the Evangelists, were lost during the remodelling of the church in the 17th century.