Pietro Cavallini, The Apse Mosaic at Santa Maria in Trastevere: Detail: three episodes in the infancy of Jesus
Left to right in the band below the main mosaic of the apse:
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The Birth of Christ. The composition resembles traditional and Orthodox Nativities such as
this one in Sicily, but it anticipates 14th-century works in replacing the midwives with a fluting shepherd and omitting Mary's transposition of the child from cave to stable.
The Adoration of the Magi. This image reflects Matthew's statement that the Magi visited the "house" where the baby lay (Matthew 2:11). The star that guided them is above the roof of the house. The pink structure from which they have traveled is most likely Jerusalem, visualized as a short distance from Bethlehem. It could conceivably be the "top of the mountain of victory" where the Golden Legend says the three were told of the birth of the Savior, but no such structure is mentioned in the Legend or pictured in any images I know of. (The two inscriptions translate as "The infant unknown to the nations becomes known by the guiding star" and "The creator accepts myrrh, incense, and gold from the Magi."
The Presentation in the Temple. In a nice parallel, Simeon holds the baby on the right while Joseph holds the two doves on the left. Both hold these "offerings" on draped hands.
Read more about the Nativity, the Adoration of the Magi, and the Presentation in the Temple.
Photographed at the basilica by Richard Stracke, shared under Attribution-NonCommercial-ShareAlike license.