Francesco Borromini (Bissone 1599 – Rome 1667)
The staircase, probably designed by Francesco Borromini, serves the south wing of the palace, so complementing Bernini’s staircase on a principle which is not just aesthetic but also distributive and functional. Accessed by the external portico, it led to Cardinal Francesco Barberini’s rooms, and was intended for more private use.
The staircase is helicoidal, hence it follows the principle of turning on its rotational axis. It has an oval plan, flattened longitudinally, so providing easier ascent than staircases on a circular plan. The model was codified in the Cinquecento treatises by Vignola, Sebastiano Serlio and Andrea Palladio.
Each turn comprises 12 Doric double twisted columns and capitals decorated with small bees (the Barberini family’s heraldic symbol). The main axis measures 9.40 m, and the lesser axis 7.85 m. Light is shed through the oculus above as well as the windows in the façade. In the initial project, the staircase terminated in a free ramp; this was later reduced as a result of the top floor of the palace being raised to make room for Cardinal Francesco’s rich library, now transferred to the Vatican.
Spiral-shaped structures, with all the problems involved in their design, were particularly congenial to Borromini’s eccentric spirit: he devised them in several drawings and in the architectural details of other works.