"The Spanish Stairs were built to unite Via del Babuino (the easternmost of the three main arteries radiating into the city from the Piazza del Popolo) with Via Felice, the first great street planned by Sixtus V (1585). Their junction is crossed at an approximately right angle by Via Condotti, which defines the direction toward St. Peter's and the Vatican. Several projects were made between 1717 and 1720, also by Alessandro Specchi, whose ideas were later assimilated by the chosen architect of the Stairs, Francesco de Sanctis. The very rich and varied solution ultimately employed by De Sanctis (1723-26) is based on a simple doubling in depth of the central theme from the Ripetta: a protruding volume flanked by convex stairs and a straight flight in front. The upper unit presents the theme in its basic form; the lower constitutes an articulate and lively variation."

— Christian Norberg-Schulz. Late Baroque and Rococo Architecture. p28.