McGill University

Philosophy of Structures

Maria Patricia Farfan


A distinctive feature of Florence's skyline is the dome of the cathedral Santa Maria del Fiore  Florence live

The building itself, located due north of the Piazza de la Signoria, was begun by the sculptor

Arnolfo di Cambio in 1296. Numerous local artists continued to work on it during the following century and a half. The painter Giotto designed its sturdy bell tower (campanile) in 1334. Yet, the massive octagonal cupola (1420-36) that truly dominates both the church and the city was the proud achievement of Filippo Brunelleschi architect and sculptor. Opposite the cathedral stands the Baptistery; the building dates from the 11th century but was believed by Florentines to be a surviving Roman monument when the commissioned for it a series of bronze doors with relief sculptures. The third pair of these doors, by Lorenzo Ghiberti, were not so beauty than Michelangelo door called " Gates of Paradise."


The cathedral of Florence itself had been begun in the Gothic style by Arnolfo di Cambio in 1296. But in 1366 the City of Florence, following the advice of certain painters and sculptors, decided that the Gothic should no longer be used and that all new work should follow Roman forms, including an octagonal dome 42 metres in span to be built at the east end of the nave. The dome was not built until the early 15th century, when Filippo Brunelleschi, a goldsmith and sculptor, began to make statues for the cathedral. Gradually he became interested in the building itself and built some smaller parts of it. In about 1415 he prepared a design for the dome that he daringly proposed to build without the aid of formwork, which had been absolutely necessary in all previous Roman and Gothic construction. He built a 1:12 model of the dome in brick to demonstrate his method; the design was accepted and built under his supervision from 1420 to 1436.

Filippo Brunelleschi (Firenze, 1377-1446)

Architect, perspectivist, and sculptor. There’s not much information about Filippo Brunelleschi's career until 1418-20, when we he was engaged in various architectural projects for Florence: the dome of Santa Maria del Fiore, the Spedale degli Innocenti, and the churches of San Lorenzo and Santo Spirito. In this period he painted, by the aid of a mirror, two panels showing the Baptistery and the Piazza della Signori perspective. These works - now lost - marked the birth of linear perspective. Also in the same years, Brunelleschi built mechanical clocks, of which only indirect accounts survive. His work as sculptor is better documented. In fact, it was back in a competence in 1401 that he competed unsuccessfully against Lorenzo Ghiberti for the construction of the second bronze door of the Florence Baptistery.


The competition for the Florence dome
In 1418 Brunelleschi entered a new competition against Ghiberti to submit a model for the dome of Santa Maria del Fiore. Brunelleschi won the contest in 1420 with a proposal to erect the dome without wooden centering.

Brunelleschi and the dome


The construction of the dome began in the summer of 1420 and was finished by 1436. The lantern, designed by Brunelleschi, was completed after his death. The copper sphere was placed on the top by Verrocchio in 1472. The construction embodies a rigorously geometrical design.

The octagonal drum carries eight "shells." Empty spaces have been left inside each of these to lighten the massive structure. The angle ribs are not intended to provide structural support. Another notable feature is the external covering system, which consists of tiles specially designed for easy assembly and maintenance.

Dimensions and characteristics

The dome's springing point stands 177 feet above ground level, while its height from the drum base to the top is about 108 feet. The distance between two opposite edges of the exterior octagonal base is about 176 feet. The height of the lantern atop the dome is slightly more than 72 feet. The dome weighs an estimated 37,000 metric tons, and the number of bricks used in the structure may exceed four million.


Geometrical structure of the dome

Polygonal domes, such as the eight-sided dome of Santa Maria del Fiore, are more complex in their design than round domes, which are generated by rotating a quarter-circle around a vertical axis. To build a dome without the use of a supporting framework, each of the masonry rings that compose the dome must be completed in succession. This was the method used by Brunelleschi, and illustrated in the model of the masonry layers.

The bricks were laid on sloping beds. Before closing each ring of bricks, the workmen placed a row of bricks whose longer sides protruded with respect to the bricks resting on the conic surface. This arrangement, known as a herring-bone, displays a spiral profile.

The second model shows the geometric principles of Brunelleschi's dome and illustrates two other essential features. First, we can see the method used to obtain the so-called pointed-fifth curvature of the angle ribs. Brunelleschi took the circle in which the dome's inner octagon is inscribed, and divided it into five equal parts. He traced intersecting arcs with a compass opening equal to four-fifths of the circle's diameter.

 site work replica

Second, the model shows the characteristic profile of the brick beds, known as "slack line" because it resembles a loose string. The reason for this is that the brick beds all lie on the surface of an inverted cone whose axis coincides with that of the dome. The cone's vertex shifts upwards as the work proceeds. This construction method is comparable to what happens when we use a pencil sharpener. The polygonal pencil is the equivalent of the dome, while the cone-shaped opening of the device represents the dome's inverted cone design. The sharpener turns the pencil's vertical sides into conic surfaces.


 during the mass


 Giotto bell