Dome of the Baptistery Chapel (or Chapel of Baptism) (Chapelle du baptist鑢e ou du bapteme).The first chapel on the left of the church.Built after a design by Carlo Fontana (1634-1714)The guiding theme of the mosaic (by Francesco Trevisani) decoration is the administration of the Sacrament of the Holy Font. The mosaics in the cupola show the triple Baptism with water; by St. John the Baptist; with blood; of the martyrs; and with desire; of the multitude eager for the purifying bath.( Saint Peter's basilica; basilique Saint-Pierre; Petersdom. )Vatican 2019