Which Baroque church in Rome was designed by Francesco Borromini for the Discalced Trinitarians?

The Baroque church in Rome designed by Francesco Borromini for the Discalced Trinitarians is San Carlo alle Quattro Fontane.

Usually called San Carlino because of its remarkably small size, the church was Borromini’s first independent architectural commission. The Spanish Trinitarians commissioned the complex in the 1630s, and construction of the church took place mainly from 1638 to 1641. It was dedicated in 1646.

Borromini had to work on a cramped, irregular corner site with limited funds. He answered those constraints with a dynamic plan based on curves, ovals, and geometric interlocking forms. Its undulating concave-convex façade and luminous oval interior became landmarks of Roman Baroque design.

A common mix-up is with Sant’Ivo alla Sapienza, another celebrated Borromini church in Rome, or Sant’Andrea al Quirinale, which was designed by Gian Lorenzo Bernini. The “four fountains” refer to the intersection beside the church, not to a fountain inside it.