What makes San Carlo alle Quattro Fontane an important work by Francesco Borromini?

San Carlo alle Quattro Fontane is considered a landmark of Baroque architecture and a defining work for Francesco Borromini due to its innovative departure from traditional design standards. Its importance stems from several key factors:123

• Geometric Innovation: Unlike contemporaries who relied on human body proportions, Borromini based his designs on complex geometric configurations. The church features an irregular floor plan defined by convex and concave curves, creating a sense of fluid, active movement.2413
• Audacious Structural Design: Borromini combined three distinct units—an undulating lower zone, a middle section suggesting a Greek cross, and an oval dome—into a cohesive, rhythmic whole. The dome appears to float due to the clever concealment of its light sources and springing point.4
• Influence on Baroque Style: The church's undulating facade and interior spatial complexity were highly influential, setting a precedent that was subsequently adopted by other Baroque and later Rococo architects.13
• Technical Virtuosity: Built on a cramped, difficult site, the project demonstrated Borromini’s ability to integrate complex rhythms and illusionistic lighting to intensify the interior space.14