The triumphal arch is decorated with 17 tondi, 15 of them with saints' busts executed in sepia fresco and two left blank. These were executed by Eugenio Cisterna in 1920, and are based on a 17th century description of original mosaics. To left and right are stylized buildings representing Jerusalem and Bethlehem, and along the roofline are flying doves.

This apse conche was repainted by Vincenzo Camuccini in 1836.
(Another photo of the fresco here)