The “measurements” of the Complex of San Carlo alle Quattro Fontane

The Complex of San Carlo alle Quattro Fontane has been the seat of the Spanish Trinitarian Order from the first half of the seventeenth century onwards. It is undoubtedly Francesco Borromini’s most studied work above all due to its architectural and artistic excellence and the “density” created by its small size, further enhancing the geometric “invention” behind the plan. While many authoritative studies have been performed, especially on the Church, Borromini’s building deserves further in-depth research regarding the unitary design of its parts (Church, “quarto del dormitorio” and Cloister). This study surveyed and tested Borromini’s design using modern modelling techniques to verify whether it reflects the metric,geometric, proportional, organisational and functional criteria specified in the Le Costituciones de la Descalcez of the Order of the Most Holy Trinity promulgated in 1614. The results of the study are currently going to print in a comprehensive volume so this contribution will focus primarily on the geniality of the architect from the Ticino canton. Although the Order imposed the “measurements” required for different parts of the Complex, he succeeded in instilling a dynamic, vibrant force on the materials by combining the structure and decorative details, thereby dilating space based on a calculated proportional ratio between plan and elevation, while respecting contemporary building principles and criteria.