The curved lines of the backdrop create a dynamic expansion of the internal space; along this path, Roman builders in the late 16th and 17th centuries set out, first among them Della Porta, who deserves credit for having designed the double shell of Michelangelo’s S. Pietro, albeit with some modifications compared to the master’s definitive plan. Then, the timid shells set on an elliptical plan developed into true domes in a sequence where architects working in Rome from Vignola to Francesco da Volterra and even Bernini and Borromini took the lead. The curvature became even more complex, and the drum took on a plastic articulation in S. Carlo ai Catinari, in S. Andrea della Valle, or in S. Carlo al Corso in Rome; and in S. Ivo alla Sapienza, Borromini composed the dome by continuing and connecting the convex-concave sections of the perimeter structures with marvelous structural daring. Later, the dome tended to dominate with its mass the entire church, conceived as its base, and the problem of barely perceiving the internal space it enclosed from the entrance led to various modifications of plan and elevation. Outside Rome, Guarini’s domes, with their light sources carved into the shell or inserted between the two non-concentric shells, generated effects of singular scenography. With Juvarra at Superga, there was a return to the more composed and measured forms generally adopted in the 18th century.
Among 19th-century domes, heirs to tradition, one might cite those of the Gran Madre di Dio in Turin, of S. Carlo in Milan, of S. Francesco di Paola in Naples, etc. Then, the new technique pushed to its extreme consequences left in S. Gaudenzio in Novara a curious example of a drum with various superimposed orders that failed to achieve the purposes and effects required of a true dome. As the perception of space changed, domes seemed destined to fade with the rise of reinforced concrete; later, they re-emerged from the formal multiplicity of 19th- and modern-century eclecticism with new interpretations of Romanesque tiburia, and finally, once again, a few domes in the wake of 16th-century tradition. — See plates LXIX–LXXII.