Originally, according to tradition, depicted in the dome was the image of St Peter, symmetrical to St Paul, depicted in the right apse of the Diaconic. Some studies put forward the hypothesis that the image of St Andrew is the result of changes made as early as the 12th century. The Saint was, in fact, revered as the founder of the Eastern Church and his presence could be seen as a political choice to show equal dignity to the Latin Church, represented by St Paul, and the Byzantine Church. Other studies support the hypothesis that St. Andrew was added to the mosaic depicting St. Paul in the 16th century, at the same time as partial renovations were carried out.
