On the triumphal arch The Heavenly Jerusalem is depicted as a walled and gated enclosure with its golden walls set with jewels. On the left side the city gate is guarded by an angel, and with another escorting saints through flowery meadows. Below this composition, is a crowd of people holding crowns and palm branches. These are the multitude of the martyrs. The mosaics are damaged by the insertion a of little balconie in front of reliquary cupboards from the changes made by St. Charles Borromeo in 1575.