The slightly elliptical dome in the transept was designed by Francesco da Volterra. The fresco, Glory of the Father, by Cristoforo Roncalli, from 1605. An illusion of added height is given by the balustrade painted along the side, leading the viewer’s gaze upwards. The dome sits on pendentives defined by the triumphal arch at the end of the nave and the three arches of the apse and the two transept chapels. In the pendentives are frescoes of the Four Evangelists, also painted by Roncalli.