In 1421 Brunelleschi began the works of the sacristy (now called the Old Sacristy) of the church of San Lorenzo (Florence), a project financed by the Medici family, and finished by 1429. Its floor plan is in the form of a perfect square and the space is covered by a dome on pendentives, this dome is an umbrella type dome, composed of 12 vaults joined together at the center. One of the four walls of the sacristy (the south wall) opens to an also square small altar which is connected to the main space by an arched opening and in turn it’s also covered by a smaller dome. This spatial design is an almost mathematical demonstration of one of the fundamental principles of perspective: the multi-dimensionality of space. By giving the greater space (the sacristy) and the minor (the altar) the same cubic scheme and the same dome cover, Brunelleschi emphasized that both spatial units were equal and that their difference, purely quantitative, depended on the apparent distance, that is on perspective. That is why the cubic space of the chapel is thought of as a distant space, just as if it were an intersection of the “visual pyramid” closest to the “vanishing point”. The interior of the main space is articulated with that of the altar by using pilasters and arches that emphasize the space’s geometric unity. The pilasters are for purely visual purposes, and mark the border between the spaces delimited by the cubes of the sacristy and the altar. These built-in pillars, together with those on the angles, the frieze and the arches are built with the so-called “pietra serena“, dark gray in color, in order to highlight their presence over the plain white surface of the walls. The pilasters support an entablature, whose purpose is to divide the space into two equal horizontal zones: the upper zone with the dome and pendentives, and the lower zone with the squared space. The pilasters showcase Corinthian capitals, also as a testament to Brunelleschi’s studies of ancient Roman architecture. The sacristy’s decorative details were by Donatello, who designed the tondoes in the pendentives, the lunettes, the reliefs above the doors and the doors themselves. The smaller dome above the altar is decorated with astrological depictions of star constellations by Giuliano d’Arrigo. Beneath a central dome lay the tombs of the donor, Giovanni di Bicci de’ Medici and his wife Piccarda Bueri.
Around 1423, while the sacristy was being built, Brunelleschi began to work in the church of San Lorenzo. Its interior, with three naves divided by two long rows of columns, resembles that of the primitive Roman basilicas, but a more careful examination allows us to notice that in this interior space the theme of the portico of the Hospital of the Innocents has been developed symmetrically: the two lateral naves repeat the succession of arches and spatial cubes projected in depth, while the central nave (much brighter) is equivalent to outer space. The viewer then has the magical impression that there is a mirror placed along the axis of the central nave that reflects, one on another, the deep perspectives of the lateral naves, exactly matching both images. In San Lorenzo, the massive pillars of Gothic architecture were replaced by slender columns with Corinthian capitals, and the traditional vaulted ceiling of the central nave was in turn replaced by a coffered ceiling with delicately gilded trimmed square compartments.
If we consider now the “cubic” sections of the lateral naves, at the wall-side of which an arch opens way to a small chapel, we will see that the ratio between the arch of the central nave and that of its corresponding chapel is 5 to 3. These figures show that both arches have a common “vanishing point”, and that for the viewer located in the middle of the central nave contemplating one of these sections, the two arches are presented as two successive intersections of the “visual pyramid”. The arches and the shaft of the columns are built in the typical dark gray “pietra serena” to underline the role they play as essential articulation elements in the succession of spaces. The same proportional graduation regulates the distribution of the intensity of light: the lateral chapels don’t have openings to the exterior, the sail vaults of the lateral naves (as those of the portico of the Hospital of the Innocents) receive a nuanced light coming from an oculi or small circular window located at the top of the arches of each chapel, while the central nave is immersed in a uniform high luminosity provided by its larger windows that run parallel to the nave over the columns.
A curious novelty of San Lorenzo which gives it rare elegance, is the arrangement of cubic pieces of entablature (with architrave, frieze and cornice) on top of each capital. This arrangement, reminiscent of the great Romanesque and Byzantine abacuses, provides an aerial grace precisely located in the area between the capital and the arch where the forces of weight and resistance meet. The Basilica of San Lorenzo is considered a milestone in the history of the development of Renaissance architecture, and one practice of Brunelleschi (in the Old Sacristy), which later became a doctrine of Renaissance architecture, was the use of white walls in churches.
The other basilica that Brunelleschi designed in Florence, the new Basilica of Santo Spirito (begun in 1444), has also three naves separated by rows of columns in “pietra serena” which in turn support arches of the same material. As in the Basilica of San Lorenzo, cubic pieces of entablature were also placed between the column capitals and the starting point of arches. Despite their similarities, this building shows new and surprising advances in the control of space. The height of the central nave is exactly twice its width, and its width is the same as the height of the arches and the distance between them and the flat roof of the central nave. On the other hand, the sections of the lateral naves have the same length as width (that is, they form a square), but their height, as in the central nave, is twice its width. It’s possible that the visitor who walks inside this church doesn’t immediately become aware of such proportions, but these do exist and contribute to creating an impression of order and serenity. As seen, Santo Spirito is also an example of the mathematical proportion and harmony omnipresent throughout Brunelleschi’s work, and is as well considered as one of the preeminent examples of Renaissance architecture.
The big difference with respect to San Lorenzo is that in Santo Spirito the side chapels are reduced to simple niches; also, the ratio between the arches of the central nave and those of the side chapels –which in San Lorenzo was 5 to 3– in Santo Spirito is 1 to 1, which means that the lateral spaces are not graduated in perspective as if they were two successive intersections of the “visual pyramid”, but they are directly articulated with the arches of the central nave by means of the transverse arches of the lateral naves. In sum, the whole space forms a reticulum of dynamic elements built with the dark “pietra serena” that totally eliminates the importance of flat surfaces. Additionally, instead of the grooved pilasters that in San Lorenzo created a separation between the side chapels, in Santo Spirito Brunelleschi placed half recessed columns supporting the arches of the side niches and joined them to the transverse arches, that is, instead of producing a pause between every two niches, the dynamics of the whole supporting structure appears to be accentuated to the maximum: the columns then become an autonomous plastic element that creates space around itself.
Between 1430 and 1444 (two years before his death), Brunelleschi directed the works on the Pazzi chapel located in the first cloister of the Basilica di Santa Croce in Florence, a work commissioned by Andrea Pazzi of the powerful Pazzi family, and whose purpose was to serve as the Chapter House or meeting place for the monks. Brunelleschi was responsible for the building’s plan, but scholars debate whether he was or wasn’t involved in the building’s execution and detailing. The inspiration for this famous chapel was the floor plan of the old sacristy of San Lorenzo, with the difference that in here the dome doesn’t rest on four walls, but on two walls and two arches, and that the floor plan was not square but rectangular, which makes it appear slightly less balanced than the old Sacristy of San Lorenzo. As in San Lorenzo’s sacristy, the Pazzi chapel includes a small cubic space reserved for the altar which repeats the lines of the small altar of San Lorenzo. The small dome on pendentives that covers the altar of the Pazzi chapel looks like a reduction of the dome that covers the larger rectangular space, which includes four ceramic medallions of the Evangelists thought to be modeled by Donatello. The walls are soberly decorated by other blue and white medallions by Luca della Robbia representing the seated Apostles. Della Robbia also did the terracotta decorations in the cupola of the porch. These medallions are accompanied on the walls by grooved pilasters of “pietra serena” that stand on a step. Inside the space of the Pazzi chapel, perfect as a diamond, there are no shadows: light comes downward from the circular windows of the dome, and changes throughout the day, this fine light that spreads over this marvelous architecture doesn’t seem to be a physical light, but a spatial light, as absolute as space itself.
The Pazzi chapel is the only work of Brunelleschi that has an exterior facade. Its centerpiece looks like a triumphal arch, with six columns with Corinthian capitals supporting an entablature decorated with medallions, over it there’s an upper level like a frieze divided by pilasters and a central arch, all of this topped with another band of sculpted entablature and a cornice at the top. Internally, this portico is covered with a barrel vault interrupted by a central coffered dome. The function of this facade is to separate the unlimited space full of sun of the exterior, from the geometric universe of the interior of the chapel; that is why its ornate vaults and its small dome create a twilight zone between them and allow in the interior only a high and uniform light that doesn’t cast shadows: the calm light of reason that Brunelleschi so much loved.
Oculus: (Plural oculi, from Latin oculus, meaning “eye”). A circular opening in the center of a dome or in a wall. Originating in antiquity, it is a feature of Byzantine and Neoclassical architecture.
Pietra Serena: A gray sandstone used extensively in Renaissance Florence for architectural details. The material obtained at Fiesole (Italy) is considered the best, though it is also quarried at Arezzo, Cortona, and Volterra.