The Church of Saint Charles at the Four Fountains (Italian: Chiesa di San Carlo alle Quattro Fontane also called San Carlino) is a Roman Catholic church in Rome, Italy. The church was designed by the architect Francesco Borromini and it was his first independent commission. It is an iconic masterpiece of Baroque architecture, built as part of a complex of monastic buildings on the Quirinal Hill for the Spanish Trinitarians, an order dedicated to the freeing of Christian slaves.
He received the commission in 1634, under the patronage of Cardinal Francesco Barberini, whose palace was across the road. However, this financial backing did not last and subsequently the building project suffered various financial difficulties. It is one of at least three churches in Rome dedicated to San Carlo, including San Carlo ai Catinari and San Carlo al Corso.
he concave-convex facade of San Carlo undulates in a non-classic way. Tall corinthian columns stand on plinths and bear the main entablatures; these define the main framework of two storeys and the tripartite bay division. Between the columns, smaller columns with their entablatures weave behind the main columns and in turn they frame niches, windows, a variety of sculptures as well as the main door, the central oval aedicule of the upper order and the oval framed medallion borne aloft by angels. Above the main entrance, cherubim herms frame the central figure of Saint Charles Borromeo by Antonio Raggi and to either side are statues of St. John of Matha and St. Felix of Valois, the founders of the Trinitarian Order.
The plan and section show the layout of the cramped and difficult site; the church is on the corner with the cloister next to it and both face onto the Via Pia. The monastic buildings straddle the site, beyond which Borromini intended to design a garden.
The church interior is both extraordinary and complex. The three principal parts can be identified vertically as the lower order at ground level, the transition zone of the pendentives and the oval coffered dome with its oval lantern. In the lower part of the church, the main altar is on the same longitudinal axis as the door and there are two altars on the cross axis. One altar is dedicated to Saint Michael de Sanctis, the other dedicated to Saint John Baptist of the Conception. Between these, and arranged in groups of four, sixteen columns carry a broad and continuous entablature.
The arrangement seems to refer to a cross plan but all the altars are visible as the two central columns in each arrangement of four are placed on the oblique with respect to the axial ordering of the space. This creates an undulating movement effect which is enhanced by the variation in treatment of the bays between the columns with niches, mouldings, and doors. Architectural historians have described how the bay structure of this lower order can have different rhythmic readings and the underlying geometric rationale for this complex ground plan, as well as discussing the symbolism of the church and the distinctive architectural drawings of Borromini.