The mosaic programme on the triumphal arch at Santa Maria Maggiore is dated to the pontificate of Sixtus III (430-40). The four registers (left side, from top) depict the annunciation, the visit of the magi, the massacre of the innocents, and Jerusalem.
On the right of the arch, the four registers depict the presentation in the Temple, a scene from the flight to Egypt, Herod and the magi, and Bethlehem.
The annunciation to Mary is depicted with five angelic figures who represent a sequence corresponding to the key moments of the Lukan annunciation narrative. Mary’s weaving is a detail that also occurs in the noncanonical Infancy Gospel of Matthew, a Latin text closely related to the Greek Protevangelium of James.
The Matthean annunciation to Joseph is represented in seamless transition from the Lukan annunciation to Mary. The greater prominence given to the annunciation to Mary suggests a prioritization of Luke over Matthew in chronology and significance, though both announcements are parallel. The rod held in Joseph’s hand derives from the Infancy Gospel of Matthew, and it symbolizes Joseph’s divine commission as Mary’s protector.
Peter and Paul stand on either side of an empty throne with a superimposed cross. Holding open books, they appear to be preaching. The inscription below refers to Sixtus III, bishop of Rome, who embodies the ministry of Peter and Paul. The inscription describes Sixtus as EPISCOPVS||PLEBI||DEI (“Bishop to the People of God”). At the foot of the throne is the scroll with seven seals from Revelation 5.1-10, and encircling the throne is a medallion representing the “rainbow around the throne” of Revelation 4.3. The four winged creatures are seen in profile on either side, bearing wreaths representing their praise of the Lamb (Rev 5.8-9). There is no visible connection to the gospels.
Incorporated within the presentation scene (here showing Simeon and a procession of priests) is the Matthean warning to Joseph to flee to Egypt. This sequence corresponds to the Luke-Matthew sequence of the annunciations on the left side of the throne, as well as to the calf and human also to the left of the throne.
The Matthean magi, led by a star, bring their gifts to the enthroned Christ-child, while the Lukan angels sing their hymn of praise, two looking heavenward and two earthward. Unusually Mary is seated at a distance from her child, while on the right sits the Sybil of Cumae referred to in Virgil’s fourth Eclogue, read by Christians as a messianic prophecy.