In the east and west lunette of the central tower, at the feet of the two Apostles, rests a pair of graceful doves, perched on a basin filled with water. One drinks, barely rippling the water caressed by the light and casts its shadow, while the other looks away. They stand out against a deep indigo background. It is an image of serenity, where sinuous dark tesserae and their volumes define the contours through a skilful play of glazes in varying tones, with the whites marking the points of greatest brightness.
This iconography has ancient roots, also mentioned by Pliny the Elder in his description of a mosaic realised by Sòsos, a mosaic artist active in Pergamon in the 2nd century BC. In the Mausoleum of Galla Placidia the doves are to be interpreted symbolically. They embody the Christian soul at the moment of its passage into the Afterlife, finding solace in water – the source of life and celestial peace.