San Carlo alle Quattro Fontane
A small church on a cramped site at a crossroads. Borromini made the façade undulate in curves – concave, convex, concave – and covered the interior with an oval dome coffered with crosses, octagons and hexagons. It is Baroque movement in concentrated form.
The patron was a small and poor Spanish order, the Discalced Trinitarians, which in 1634 commissioned Francesco Borromini to build a monastery and church on a cramped corner site at the Quattro Fontane crossroads. It was Borromini’s first independent commission. The monastery building and the small cloister were built first, then the church, which was finished in the early 1640s. The façade was only added at the end of his life, in the 1660s, and was completed after his death in 1667. The church is dedicated to Carlo Borromeo, the canonised Archbishop of Milan. The building materials are simple: brick and stucco, and instead of coloured marble and gilding Borromini created his effects with white stucco, light and complex geometry.
The plan is based on geometric figures: two equilateral triangles that together form a rhombus, with an oval inscribed in it. The walls undulate in and out, and the columns stand close together in groups so that the space seems to be in motion. The dome is oval and covered with coffers in the shape of crosses, octagons and hexagons, which grow smaller towards the top and make the dome look higher than it is. Light comes from hidden windows at the base of the dome and from the lantern, where the triangle of the Trinity can be seen. The cloister is small, with chamfered, curved corners. The façade has two storeys: the lower part curves concave, convex and concave, while the upper part has three concave bays and is crowned by a medallion carried by angels.
The church attracted attention at once. The order proudly reported that visitors from many countries asked for drawings of it. Borromini’s way of letting geometry govern the entire space became highly influential, first with Guarino Guarini in Turin and then in the Baroque of Bohemia, Austria and southern Germany, where architects such as the Dientzenhofer family built on his undulating walls. In Sweden Borromini had less influence. Nicodemus Tessin the Younger, who studied in Rome, admired above all Bernini and the more classical Roman and French Baroque. San Carlo has since been restored, and the façade has been cleaned. It remains one of the finest examples of how Baroque architecture could create movement and light in a very small space.