The upper mosaic of the conch represents Christ standing in the middle, flanked by St Felicissimus, St Mark the Evangelist, Pope Gregory IV (with the squared halo of the living people, holding a model of the church, which he restored following a severe flood) on the left and Sts Pope Marcus, Pope Agapitus and Agnes on the right. St Mark has his hand on Pope Gregory's shoulder, meaning that he is introducing him to Christ.