The orderly ensemble of the many mouldings that make up the outer walls of the apses is formed by ogival arches, lower in height, which intersect each other on the same axes with a sinuous rhythm, almost as if to compose a silent melody. The contrast of colours seems to form the musical accompaniment, animated by the notes of the brown limestone, the grey-black lava tuff from Vesuvius, and the red bricks used in the thin horizontal bands. Softening this varied concert of colours is the warm golden-brown hue of the background.
