La spirale cilindrica nelle scale rinascimentali e barocche

The helicoid staircases are often used in the architecture since the ancient age. In the medieval period this type of stair is used into towers, fortifications or bell towers with a main functional value. Starting from renaissance the architects thought to give them also an high architectural value. The first was Bramante in Vatican (1507), then Vignola in Caprarola (1559), Mascarino in the Quirinale palace (1585) and Borromini in the Barberni Palace (1633). The architecture treatises had an important role about the diffusion of the helicoid staircases. In I Quattro libri Palladio describes several types, with circular and oval plant. The comparison of this four work of art, also thanks to recent digital surveys of three of these stairs, allowed us to highlight the relationship between the geometric matrix of the projects and their built. Each realization is an expression of own time in a long evolution of a same idea based on the helix application. In each realization there are different technical problem about the slope, the shape of the step and the way to develop the trabeation and, in general, the architectural order.