Sabatini created this staircase in 1760, and it was repaired in the early reign of Charles IV. Its construction incorporated the same marble and granite utilized in the building's other rooms.

Corrado Giaquinto painted the frescoes for the lunette vault, which is decorated with huge lighting oculi as part of Sachetti's iconographic concept to exalt the Spanish Monarchy. In them, he painted allegories that collectively depict the Triumph of Religion and the Church in the main vault, the Victory of Spain over Saracen dominance in one of the two lunettes above the door, and Hercules pulling the Pillars of Gibraltar in defiance of Neptune's might in the lunette in front, situated behind the statue of Charles IV. The virtues said to be emblematic of Ferdinand VI's rule are depicted on the cornice. At a period when it was vital to strengthen the idea of being Spanish, all of these images stand for the universality and values of the Spanish country.

Robert Michel and Felipe de Castro, respectively, are the sculptors of the lions that adorn the base of the balustrades. Robert Michel's statue of Charles IV dressed in Roman garb is located above the niche at the top of the stairway. There are busts by René Frémin of Philip V and Isabella Farnese along the corridor leading to the salons.