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The Oddity of San Carlino's Coffering

Updated: Jun 20, 2020

A Manifesto to Borromini's Legacy

Tucked into a corner of the intersection between Via del Quirinale and Via Venti Settembre lies San Carlo alle Quattro Fontane, a truly remarkable church. To the viewer who passes by, the façade presents a remarkable testament to the beauty of the Baroque. But to the one who enters, San Carlino offers even greater wonders. Although small in size, the church’s ceiling rises high above the viewer in the form of a white dome decorated simply with geometric coffering (Figures 1 and 2). Initially, the aesthetic effect overpowers any questions regarding the architect’s intent, but when the dome’s coffering is subjected to further examination its oddity becomes unavoidable.

Figure 2. Borromini, San Carlo alle Quattro Fontane, Rome, accessed April 19, 2018, Artsotr.

The geometric design and its complete lack of ornamentation are unusual, raising the question as to why Borromini chose to decorate the dome of his first independent commission in such an untraditional manner. Ultimately, there are three general explanations for the coffering of San Carlino’s dome: practicality, geometric symbolism, and artistic identity. However, based upon thorough research and analysis, the latter explanation becomes the most plausible. The coffering of San Carlino’s dome functions as an intimate declaration of Borromini’s authorship of the church and embodies a manifesto to his artistic preferences and architectural prowess.

Before looking into the potential interpretations of the coffering, it is necessary to recognize the oddity of the coffering by considering its origins. The source of its design is thought to be from “a field of mosaic decoration on the ring vault of Sta. Constanza.”[1] Another potential source of the design was a similar pattern used in the late 15th C. barrel vault decoration at the Santuario dell-Incoranata at Lodi.[2] Steinberg rightfully observes that, “we may justifiably ask why he dressed his first dome in a pattern that had long been in the public domain.”[3] Considering how this was a familiar design, it seems odd that Borromini chose to feature it so predominantly in San Carlino. The three potential reasons for its use are as follows: it could have been for practicality, for the sake of symbolism, or for personal and artistic reasons.


The starting point for an accurate interpretation of San Carlino is its commissioners, who were at the heart of San Carlino’s purpose. Prior to the commission, Pope Paul V decided that the Spanish Trinitarians should take Carlo Borromeo “the Milanese bishop as their dedicatee.”[4] Thus in 1634 “the barely solvent Spanish Trinitarians commissioned the as yet untested Francesco Borromini to design a new convent in Rome, along with a church dedicated to San Carlo Borromeo and the Holy Trinity.”[5] Consequently, the Spanish Trinitarians were not prosperous at the time when San Carlino was built.[6]

The decoration of the dome may have been limited because of financial and material restrictions. The Spanish Trinitarians simply may not have been able to afford frescos or marble. This theory is further supported by the fact that the only marble in San Carlino is in its architrave, which is surrounded by stucco-covered brick that was “polished in such a way as to create the illusion of a continuity with the central marble block.”[7] While aesthetically simple, San Carlino’s white dome gives the illusion of marble even though it is constructed from stucco, a much cheaper material.

Because of their limitations in funding, San Carlino was built in a small and awkwardly shaped space and Borromini had to find a way in which “to fit everything – church, cloister, apartments, and garden – on a small and irregular site […] The solution was provided by geometry, which allowed each part to flow from the other.”[8] Stucco coffering, like in San Carlino’s dome, was commonly used on flat ceilings or barrel vaults throughout the church, particularly in its side aisles.[9] Because of its restricted space, Borromini constructed San Carlino as a stretched oval without side aisles or a transept, the places where barrel vaults would generally be used.

By adding coffering to the dome, Borrromini may have attempted to abbreviate the familiar elements of a church in order to maximize the space. But while this is a viable interpretation, it has a significant flaw that makes it an inadequate conclusion on its own. The dome generally epitomizes the apex of the church since it functions as a holy and set-apart space. While practicality may have been a contributing force in the decision to feature coffering in the dome, it is unlikely that this was its sole purpose.


During the Baroque period, religious symbolism became a focal point for artists and architects. The curvature of San Carlino’s façade, its interior, and the range of natural lighting in the dome emphasized by the scarcity of color are all mechanisms for communicating religious meaning. According to Cipriani, baroque religious art “became the vehicle for a new, more dynamic, outpouring of religious fervor.”[10] San Carlino was built in the midst of this movement as a concentrated embodiment of these ideals. Even in its most simplified form, San Carlino’s plan conveys a plethora of symbolic statements.

The overall shape of the chapel mirrors that of a mandorla: “the auric vessel and window into heaven that had become a ubiquitous ideogram in Christian art.”[11] A mandorla resembles the space between two overlapping circles, like in a Venn diagram. The mandorla came to represent a convergence between heaven and earth, the divine and the physical.[12] In choosing to shape San Carlino like a lobbed mandorla, Borromini attributed to San Carlino the function of bringing together the earthly and the divine, humanity and their God.

Likewise, he explored the nature of his God and the ownership of the church by creating the mandorla from three shapes. As Steinberg states, San Carlino possesses a triform plan in reference to the biblical Trinity. In most oval churches, the architects limited the nave of their church to a simple oval and clearly delineated the nave of the church from the side chapels. However, San Carlino possesses “a sinuous wall whose alternating concavities and convexities enclose both the nave and its niches.”[13]

This stylistic decision begins to reveal the basic structure of San Carlino’s plan, which is a combination of an oval, cross, and octagon.[14] The octagon is visible in the outline of the cloister and four axial chapels, but can be seen most clearly in the plans. [15] The cross appears in the side chapels that give the illusion that there are four barrel-vaulted cross arms extending from the center of the church.[16] Lastly, the oval clearly manifests itself in the dome and in the general shape of the church’s interior.[17]

According to the geometry of Borromini’s time, the circle and oval were attributed with divine qualities. Mathematicians sought ways to theoretically explain and recreate perfect ovals and circles and, in turn, architects became fascinated with these forms. For example, the highly influential architect Alberti claimed that, “The circle seems therefore to be the ultimate reference, since it is – Alberti states – the favourite shape of nature.”[18] Borromini, in designing San Carlino, began his plans with an elongated cross and with that he created a “synthesis of cross, oval, and octagon.”[19]

Functionality necessitated that San Carlino include a cruciform shape. San Carlino’s limited space could not have functioned as a perfectly central plan otherwise there would not have been enough room for processions and other basic liturgical processes. It was both practical and innovative to marry the traditional function of the church with a central plan and then to crown the structure with an oval dome. “By stretching the central circle into an oval, longitudinality is added to the building, without cancelling the feeling of centrality.”[20] This combination led to further symbolic resonance as the oval indicates “cosmic centrality” while the cross represents “pragmatic necessities of linearity required for processions and liturgical celebrations.”[21] The octagon necessarily followed as a linear simplification of the oval, creating a smooth transition from oval to cross.

Symbolism, both geometric and iconoclastic, certainly influenced Borromini’s decision to leave the coffering bare. Steinberg argues that the coffering reiterates the triform nature of the building, unifying the dome to the rest of the church in its “triform interpretation.”[22] The octagon, cross, and circle reappear in the coffering of the dome, and in the lantern they visually emerge in the octagonal shape of a sunburst, in the cross-like form of the dove, and in the circle around the dove (Figure 3).[23] Additionally, a triangle surrounds the dove as another reference to the Trinity. Combined, these elements appear to support the view that Borromini, who was iconoclastic, “aimed to venerate God through geometry that emphasized the rationality of nature.”[24]

While this description is plausible in general, it can become a narrow interpretation that contradicts with other aspects of San Carlino and undervalues a holistic view of Borromini’s motivations as an artist. If the purpose of San Carlino’s coffering was simply to symbolically unify the dome with the rest of the church, then its function would have been redundant since San Carlino’s lantern was already fulfilling that role. Previously, Borromini had designed and constructed the lantern of Sant’Andrea della Valle.[25] Through the lantern, “Borromini was able to pull the entire dome complex together organically as he rethought the whole articulation of drum, dome, and lantern.”[26] In this same way, San Carlino’s lantern sufficiently connected the dome to the rest of the church. This means that if the coffering’s purpose were solely symbolic then it was rendered both unnecessary and even distracting in conjunction with the lantern.

Regarding the lack of ornamentation and representational imagery in the dome, Borromini, despite his iconoclastic tendencies, had a favorable view towards the paintings that were in San Carlino. These included the high altarpiece, originally by Orazio Borgianni and later replaced by a painting by Pierre Mignard.[27] Mignard also painted an Annunciation for the internal façade, which Borromini particularly liked because of its symbolic connotations.[28] Borromini’s appreciation for the paintings in San Carlino simply contradicts with the idea that the lack of decoration in the dome was entirely dictated by Borromini’s iconoclasm. In the end, the unornamented coffering of San Carlino’s dome was not solely intended for practical or symbolic purposes. Rather, the coffering possesses unique qualities that identify San Carlino as Borromini’s work.

Artistic Identity

San Carlo alle Quattro Fontane became a personal testament to Borromini’s talent and preferences as an architect. The façade and dome exemplify his genius and ability to reinvent the familiar. His respect for Maderno, Michelangelo, and Borromeo demonstrate his attachment to the commission and particularly to the coffering. The contrast between San Carlino and its copy, S. Maria del Prato in Gubbio, shows what the church would have been like without the coffering. Combined, the weight of these proofs along with accounts of Borromini’s possessive nature create a strong case for the third interpretation, which is that Borromini made the coffering as a personal manifesto.

The commission for San Carlo alle Quattro Fontane represented a major transition in Borromini’s career and is, arguably, his finest work. The interior of the church was constructed during his lifetime under his direct control and, consequently, exists as an ideal example of his artistic style. Into the church Borromini “packed ‘all he knew’ to produce ‘an extraordinary design, with nothing copied or borrowed from any architect, but founded on the antique and on the best architectural authors.”[29]

Entering San Carlino “is a dizzying experience. Shapes morph into one another. A convex curve suddenly becomes concave, and it is impossible to determine exactly how or where the transformation took place.”[30] The geometric concoctions that Borromini invented were an amalgamation of classical and innovative architecture “that was defined by organically curving lines and a complicated interplay of geometric forms.”[31] The interchange between curved and rigid forms in San Carlino was unusual for its time and “Borromini was considered by succeeding generations of architects to be too radical and excessive.”[32] Despite the grievances held against him, Borromini’s genius could not be denied. In particular, the façade and dome of San Carlino exemplify his architectural ingenuity.

Figure 4. Borromini, Façade of San Carlo alle Quattro Fontane, Rome.

Although the façade was completed last, drawings of the façade of San Carlino provide evidence that Borromini planned from the beginning to have the façade reflect the movement of the church’s nave (Figures 4 and 5).[33] While simple in theory, the execution of this design proved difficult to implement. San Carlino’s façade is “one of the earliest, as well as one of the most mature, examples of the fully curved Baroque façade.”[34] Borromini based the relationship between the façade and the interior of the church on decades of research. This allowed “Borromini to express his personal talent fully by designing a curved street front, whose flowing lines echo and extend the sinuosity of the interior walls.”[35]

Figure 5. Borromini, Façade of San Carlo alle Quattro Fontane, Rome.

Moving within the church, the viewer can begin to observe the bond between the façade and the form of the nave. The oval dome, featured in the heart of this small church, creates an illusion of centrality while maintaining liturgical functionality. The symbolic value of centrality is that, “In centrally planned churches, the dome rises over the heads (and souls) of the worshippers, thus creating a different spatial relationship between the single individual and the house of God.”[36] The central plan, crowned with a dome, leaves room above and surrounding the viewer, creating an illusion of openness and grandeur. In turn, the emptiness becomes a divinely charged environment that envelops and aids the worshipper.

The oval dome also references mathematical ideals and some historians see the oval dome of San Carlino as the application of “the new science of Kepler and Galileo.”[37] The Keplerian revolution endorsed the use of oval forms in church architecture because it claimed that, “the circle and the ellipse were wholly interchangeable; neither one metaphysically or pictorially privileged.”[38] This mathematical concept is relevant to the oval dome of San Carlino and coincides with Borromini’s philosophy of geometry. As Perez states, “Forms are alive for Borromini. If he mixes them, it is because, according to him, they partake of a non-exclusive metaphysics of becoming.[39] While the oval dome of San Carlino condenses the traditional church structure, it also allows the church to exist within a state of perpetually ‘becoming’ both a central and a cruciform plan.

Borromini had a passion and genius for complex architecture. Even though the pattern of the coffering in San Carlino’s dome was relatively common during Borromini’s time, this was the first time that it was employed on an ellipsoidal surface, which significantly added to the difficulty of its construction.[40] In addition to this, he chose to layer the coffering by nestling shapes into one another, adding new forms and complexity.[41] Although Borromini possessed immense architectural talent, he was obsessed with his reputation to the point of being described as, “neurotic, difficult, touchy, suffered from something very near persecution mania, and quarreled with most of his patrons and friends.”[42] He consistently sought recognition for his excellence and hated the thought of his own work being attributed to others. While the shapes used in the coffering do align with San Carlino’s triform plan, Borromini reinvented the coffered pattern and employed it strategically as an assertion of his excellence.

Borromini may have been exceptionally competitive and socially inept, but he was dogmatic in his respect for three people: Maderno, Michelangelo, and Carlo Borromeo. His admiration for these three individuals manifested itself in San Carlino, demonstrating the personal attachment he had to the commission. Although Borromini did not receive an education in his craft, he did have the opportunity to work under the renowned architect Maderno who entrusted Borromini with various important projects that refined his skills. Borromini began his career as a stucco-worker, but with time he became one of Maderno’s most trusted workers and eventually was chosen to be his chief draughtsman when Maderno was commissioned to make the Palazzo Barberini.[43]

When drawings of a pattern similar to that of the coffering in San Carlino spread throughout Europe, Maderno chose to incorporate it in his work in St. Peter’s “on the segmental vaults between the domed bays of the aisles.”[44] Borromini may have become familiar with the pattern because of his connection with Maderno or he may have been drawn to it during one of the many trips he took to St. Peter’s to study the architecture of Michelangelo.

Borromini greatly esteemed Michelangelo as Frances explains in the following statement:

No one comprehended the innovations of Michelangelo’s architecture better than Borromini, and at St. Peter’s Borromini spent all of his spare time making drawings after Michelangelo while others denigrated the architecture of the sixteenth-century master.[45]

In fact, many aspects of San Carlino possess characteristics of classical architectural elements that particularly resemble St. Peter’s.[46] Connors states that in San Carlino, “The piers with their pendentives and arconi recall, most obviously, St Peter’s.”[47] While the difference in size between San Carlino and St. Peter’s is massive, “Through structural similarity and quantitative agreement the tiny church at the Four Fountains was rendered St. Peter’s child.”[48] In particular, the circumference of San Carlino’s “cupola at its base measures exactly 186 Roman palmi – and Vasari gives 186 palmi as the diameter of Michelangelo’s dome.”[49] Steinberg pronounces San Carlino as an abbreviation of St. Peter’s and suggests that the coffering of the dome may mimic the barrel vaults of St. Peter’s, “All of which confirms the impression that S. Carlino offers an image in little of the Basilica’s crossing.”[50] The fact that Borromini crafted San Carlino in reference to St. Peter’s cannot be ignored since it exemplifies Borromini’s intentionality with and personal attachment to San Carlino.

Borromini’s appreciation for Michelangelo was matched only by his devotion to San Carlo Borromoeo, “the patron saint of Milan.”[51] Borromini esteemed Carlo Borromeo to such an extent that he dressed in a Spanish style and eventually changed his name from Francesco Castelli to Borromini, “one that alliterated with the Milanese saint,” in 1628.[52] In fact, Borromini’s namesake was the saint for whom San Carlino, Borromini’s first major commission, was built. Combined, these three individuals considerably influenced the creation of San Carlino and each played a significant role in Borromini’s life. The fact that the pattern used in the coffering of San Carlino’s dome closely resembles the coffering in St. Peter’s cannot be coincidental. Rather, there seems to be a powerful case for believing that there were personal motivations for the coffering.

This conclusion is further supported by analysis of San Carlo alle Quattro Fontane’s odd twin, S. Maria del Prato in Gubbio. For centuries after its construction, San Carlino remained a mystery, rejected for its unconventionality. Some of those who appreciated it tried to reproduce San Carlino, mostly without success. The only remaining copy is the S. Maria del Prato in Gubbio, which differs from San Carlino in a multitude of ways, but most significantly in its treatment of the dome. The interior roughly matches the dynamic shape of San Carlino. However, the coffering of the dome was filled and covered in frescos since the architect in charge of building S. Maria del Prato decided to hire an artist to paint the frescos for the sake of the prestige that it would bring the church.

Sprelli could count on the services of Francesco Allegrini, the best baroque fresco painter that anyone could ever hope to attract to Gubbio. […] So the coffered zones of the model, the cupola and the vaults of the four nicchioni, were replaced in Gubbio by smooth vaults entirely covered in fresco.”[53]

The frescos produce an altered atmosphere with a greater emphasis on the paintings than on the architecture. Sprelli may have felt the need to make the space unique since the building was a copy of another architect’s work. This pressure undoubtedly was present for both architects, as the challenge of artistry is to make something that is unique and showcases the artist’s skill and taste. For Borromini in particular, who was obsessed with his reputation, he could not have risked featuring another artist’s work as the capstone of his first major commission.

Borromini’s distrusted nearly everyone, which motivated him to refuse to publish any plans for San Carlino. He was paranoid that others would receive credit for his own work, so around 1660 when he did publish plans for S. Carlino he made ones that “idealise the church and smooth over the many difficulties and changes of plan that marked its construction.”[54] Additionally, before his death Borromini burned most of his drawings of San Carlino so that his rivals would not be able to use them and “no geometrically explicit plans of S. Carlino were published until this century.”[55]

When considering the coffering of San Carlino’s dome, it is necessary to remember that this was the same man who destroyed the plans for San Carlino in an attempt to maintain ownership of his ideas. Sprelli, in building S. Maria del Prato, became Borromini’s foil. He may have been able to replicate Borromini’s work, but it was not his own and he concealed that inadequacy with a frescoed dome. In essence, the coffering of San Carlino’s dome became an expression of Borromini’s architectural genius and artistic preferences.


The design and construction of San Carlino were inexorably tied to Borromini’s identity. While the Spanish Trinitarians did have limited means that restricted the funds for building San Carlino, it is unlikely that Borromini would have chosen the dome’s design solely for that reason. He did feature geometry in the church for mathematical reasons and for the sake of religious symbolism; however, if these were his only reasons the coffering would have been unnecessary and could have been replaced with frescos or supplemented with more ornamentation. Along with his love for geometry, Borromini was an architectural genius, had great respect for Maderno, Michelangelo, and Borromeo, and was extremely possessive. Based on this analysis, any interpretation of the coffering of San Carlino’s dome would be incomplete without recognition of how it functions as a personal assertion, a manifesto, to Borromini’s ingenuity as an architect.



Blunt, Anthony, Alastair Lang, Christopher Tadgell, Kerry Downes. Baroque and Rococo Architecture & Decoration. New York: Harper & Rowe, 1978.

Cipriani, Gabriele, Luca Cipriani, and Mario Di Fiorino. "Personality and Destiny. Francesco Borromini: Portrait of a Tormented Soul." History Of Psychiatry 28, no. 3 (2017): 352.

Connors, Joseph. “A Copy of Borromini’s S. Carlo alle Quattro Fontane in Gubbio.” The Burlington Magazine no. 1110 (1995): 588-599.

Duvernoy, Sylvie. "Baroque Oval Churches: Innovative Geometrical Patterns in Early Modern Sacred Architecture." Nexus Network Journal: Architecture & Mathematics 17, no. 2 (2015): 425-456.

Frances, Huemer. "Borromini and Michelangelo, III: The Dome of Sant'andrea Della Valle." Source: Notes In The History Of Art no. 4 (2001): 23-29.

Hill, Michael "Practical and Symbolic Geometry in Borromini’s San Carlo alle Quattro Fontane." Journal Of The Society Of Architectural Historians no. 4 (2013): 555-583.

Perez, Rolando. "Severo Sarduy on Galileo, Kepler, Borromini, and the Coded Language of the Anamorphic Image." Romance Notes no. 2 (2016): 225.

Steinberg, Leo. Borromini’s San Carlo alle Quattro Fontane: A Study in Multiple Form and Architectural Symbolism. New York: Garland Publishing, 1977.

[1] Steinberg, Borromini’s San Carlo alle Quattro Fontane, 220.

[2] Steinberg, Borromini’s San Carlo alle Quattro Fontane, 222.

[3] Steinberg, Borromini’s San Carlo alle Quattro Fontane, 223.

[4] Hill, "Practical and Symbolic Geometry,” 576.

[5] Hill, "Practical and Symbolic Geometry,” 555.

[6] Blunt, et al., Baroque and Rococo, 38.

[7] Connors, "A Copy of Borromini’s S. Carlo,” 595.

[8] Hill, "Practical and Symbolic Geometry,” 569.

[9] Steinberg, Borromini’s San Carlo alle Quattro Fontane, xi.

[10] Cipriani, et al., "Personality and Destiny,” 353.

[11] Hill, "Practical and Symbolic Geometry,” 570.

[12] Hill, "Practical and Symbolic Geometry,” 571.

[13] Duvernoy, "Baroque Oval Churches,” 440.

[14] Steinberg, Borromini’s San Carlo alle Quattro Fontane, vi.

[15] Steinberg, Borromini’s San Carlo alle Quattro Fontane, vii-ix.

[16] Steinberg, Borromini’s San Carlo alle Quattro Fontane, ix.

[17] Steinberg, Borromini’s San Carlo alle Quattro Fontane, ix.

[18] Duvernoy, "Baroque Oval Churches,” 426.

[19] Hill, "Practical and Symbolic Geometry,” 555.

[20] Duvernoy, "Baroque Oval Churches,” 427.

[21] Duvernoy, "Baroque Oval Churches,” 427.

[22] Steinberg, Borromini’s San Carlo alle Quattro Fontane, 219 and 235.

[23] Steinberg, Borromini’s San Carlo alle Quattro Fontane, 247.

[24] Cipriani, et al., "Personality and Destiny,” 355.

[25] Frances, "Borromini and Michelangelo, III,” 23.

[26] Frances, "Borromini and Michelangelo, III,” 28.

[27] Hill, "Practical and Symbolic Geometry,” 573 and 576.

[28] Hill, "Practical and Symbolic Geometry,” 579.

[29] Duvernoy, "Baroque Oval Churches,” 439 and Connors, "A Copy of Borromini’s S. Carlo,” 588.

[30] Cipriani, et al., "Personality and Destiny,” 354.

[31] Cipriani, et al., "Personality and Destiny,” 353.

[32] Cipriani, et al., "Personality and Destiny,” 354.

[33] Steinberg, Borromini’s San Carlo alle Quattro Fontane, viii.

[34] Blunt, et al., Baroque and Rococo, 42.

[35] Duvernoy, "Baroque Oval Churches,” 452.

[36] Duvernoy, "Baroque Oval Churches,” 426.

[37] Hill, "Practical and Symbolic Geometry,” 555.

[38] Perez, "Severo Sarduy on Galileo,” 228.

[39] Perez, "Severo Sarduy on Galileo,” 228.

[40] Steinberg, Borromini’s San Carlo alle Quattro Fontane, 225.

[41] Steinberg, Borromini’s San Carlo alle Quattro Fontane, 228.

[42] Blunt, et al., Baroque and Rococo, 37.

[43] Blunt, et al., Baroque and Rococo, 39.

[44] Steinberg, Borromini’s San Carlo alle Quattro Fontane, 224.

[45] Frances, "Borromini and Michelangelo, III,” 28.

[46] Connors, "A Copy of Borromini’s S. Carlo,” 595.

[47] Connors, "A Copy of Borromini’s S. Carlo,” 595.

[48] Steinberg, Borromini’s San Carlo alle Quattro Fontane, 405.

[49] Steinberg, Borromini’s San Carlo alle Quattro Fontane, 404.

[50] Steinberg, Borromini’s San Carlo alle Quattro Fontane, 404.

[51] Cipriani, et al., "Personality and Destiny,” 355.

[52] Blunt, et al., Baroque and Rococo, 39 and Hill, "Practical and Symbolic Geometry,” 576.

[53] Connors, "A Copy of Borromini’s S. Carlo,” 595.

[54] Connors, "A Copy of Borromini’s S. Carlo,” 590.

[55] Connors, "A Copy of Borromini’s S. Carlo,” 356 and 590.

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