Ellisse e ovato tondo a Piazza San Pietro. Un’esperienza di cittadinanza attiva

The aim of this paper is to describe the spatial implications of some curved geometries, from the point of view of mathematicians and architects, together. The study case shown is that of Bernini’s project for the colonnade of St. Peter’s Square, exemplary because it can be used to show the different geometric properties of an ellipse and of an ovate. The interest also lies in the traditional ambiguity of use between the two terms. If it is true that the two curves are similar in their aspect, it is also true that their plotting is very different and so are the spatial implications of this on the perceptive level. Since the difference between the two curves appears minimal, the reasons for the choosing one instead of the other must be of other type: ease of tracking, convenience in the execution on the construction yard, perceptive and spatial factors. The theme is not new and has always caught historians and critics attention and is now a topic of lively research.