Gregorian Chapel with the altar of the Madonna of Succour, the larger Chapel of theHoly Sacrament, the Chapel ofSaint Sebastianand the Chapel of thePiet.[9]At the heart of the basilica, beneath the high altar, is theConfessioorChapel of the Confession, in reference to the confession of faith by St. Peter, which led to his martyrdom. Two curving marble staircases lead to this underground chapel at the level of the Constantinian church and immediately above the burial place of Saint Peter.