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How did Francesco Borromini fit San Carlo alle Quattro Fontane into its small site?
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Francesco Borromini
Piazza Navona, Rome, with the church of Sant'Agnese in Agone, designed by Francesco Borromini, and (foreground) the Fountain of the Moor, originally designed by Giacomo della Porta and revised by Gian Lorenzo Bernini.
To fit the San Carlo alle Quattro Fontane into its cramped and difficult site, Francesco Borromini employed a highly innovative approach that prioritized complex geometric configurations over traditional architectural norms.12
His strategy involved several key techniques:
- Layered Composition: Borromini stacked three distinct units: an undulating lower zone, a middle section suggesting a Greek cross plan, and an oval dome.2
- Geometric Interlocking: He utilized a design of intersecting and interlocking ovals and circles to manage the narrow space while accommodating the dome.3
- Illusionistic Effects: To overcome the site's physical limitations, he used calculated lighting and hidden windows to make the dome appear as if it were floating in mid-air. Additionally, the geometric coffers within the dome were designed to gradually decrease in size, creating an optical illusion of greater height.23
- Structural Integration: Borromini personally guided stonecutters on-site to realize the complex, three-dimensional curves of the arches and vaults, ensuring the design could be executed within the restricted footprint.2