Architect: Francesco Borromini
Location: Rome, Italy
Date: 1634-67
San Carlo alle Quatro Fontane was Borromini's first independent commission for the Spanish order of Discalced Trinitarians. And although the interior of the church was overseen and completely designed by Borromini, the facade was actually held up because of a lack of funds. Borromini only was able to see the first story built. After his death, his nephew, Bernardo Castelli took over the construction process and made some changes to the plan. The recessing and protruding of the three bays of the facade create an undulating effect for the entire structure with four Corinthian engaged columns demarcating the start and end of each bay. Above the main entrance sit three statues of saints: the two founders of the Trinitarian Order (Saint Jean de Matha and Felix de Valois) and Saint Carlo Borromeo in the middle. The central figure is covered by two angels on each side with wings forming the top of the niche. The balustrade above the first story frames the central bay with the sentry-box covered by an oval aedicule. At the very top, an oval medallion rests above two angels carrying it on either side; the medallion contains a large fresco of The Holy Trinity Crowning the Blessed Virgin Mary. The overall result shows Borromini's creativity and "freedom in the handling of classical elements."
Sources:
"Baroque and Rococo Art and Architecture" by Robert Neuman
http://en.wikipedia.org/wiki/San_Carlo_alle_Quattro_Fontane
http://www.bluffton.edu/~sullivanm/carlo/carlo.html
http://www.bluffton.edu/~sullivanm/italy/rome/carlofontane/carlino.html
http://romafelix.com/scarlino.htm