Il disegno della cupola del San Carlino alle Quattro Fontane di Borromini: ovale canonico?

The oval that characterizes the dome of the church of San Carlino, designed by Francesco Castelli, called Borromini, is a subject that has always attracted the interest of many scholars. Many design drawings describe a geometric trace of a polycentric curve, or an oval, with a complex plot of lines, some needed to geometrical construction and correspondence with architectural drawing, others of uncertain interpretation. This study aims to investigate the actual role which has the oval shape in the project of San Carlino by comparing the design drawings and the detailed study of the model derived from the survey. In particular this study analyze the sections of the elements where the shape of the oval is present: the tiburium, the coffered dome, the lantern.