San Lorenzo in Florence was originally an eleventh-century Romanesque church. It was rebuilt in the fifteenth century and is recognized in the history of architecture as the first church designed in the Renaissance style.
The addition of monks' chapels and a choir at the liturgical east end was already underway when the main patron, Giovanni di Bicci de' Medici, brought Brunelleschi to the project. Giovanni had already commissioned him to design the Old Sacristy.
1418. Construction was begun under the Chapter's prior, Father Dolfini.
1419. Brunelleschi began working on a sacristy for the Medici family.
1421. Father Dolfini died and Brunelleschi was put in charge of the whole project, but little progress was made due to a shortage of funds.
1425. Work ceased when the continuing war with Milan, and then Lucca (1429-33), began draining local resources.
1430s. The notion of replacing the older church was completely adopted, but lack of finances continued to impede construction.
1442. Work resumed in 1442 after Cosimo de' Medici attained patronage of the main chapel, transept, and nave.
Early 1440s. More chapels were needed, so the plan was amended to include side chapels adjacent to the side aisles.
1446. Brunelleschi died in 1446, only four years after work had resumed, and Michelozzo di Bartolomeo was appointed to replace him. Many scholars believe Brunelleschi’s involvement with the project ended in 1429, upon the death of Giovanni di Bicci, and that Michelozzo and Donatello were actively working in San Lorenzo shortly thereafter.
1450s-60s. The nave was begun in the 1450s and was still under construction in the 1460s.
After 1465. After 1465. Piero de’Medici, son of Cosimo de’ Medici, was given the authority to allocate the remaining chapels on the north side of the nave to any families or citizens deemed suitable.
1516-20. Pope Leo X, the first Medici pope, initiated the building of a façade, but dropped the project in 1520, due in part to the death in 1519 of Lorenzo the Younger de' Medici, Governor of Florence and Duke of Urbino, which made the building of a mortuary chapel more pressing. Designs for the façade were made by important architects like Giuliano da Sangallo and Michelangelo. The church's entrance facing remains without a façade.
Later. The dome, which is unlike the oculus-pierced ribbed domes typical of Brunelleschi, was added later.
The original intention behind the east-end expansion was the addition of monks' chapels around the transept. Brunelleschi introduced a new prototype for the Latin-cross basilica by creating a series of identical chapels whose dimensions were determined by those of the crossing square and whose placement was symmetrical.
The crossing square was used as a module with which to determine the proportions of the other parts. Its size was repeated for the choir and transept arms, halved for the bays of the nave, and quartered for the bays of the monk's chapels and side aisles. This last dimension was halved again to form the chapels on the outsides of the aisles.
Because this system of proportions is marked off in the pattern of the stone floor, the size and shape of the Church and the rational order underlying the arrangement of its parts can readily be understood.
Brunelleschi adopted the height of the columns of the nave arcade as a module for determining the church's vertical proportions. He decided that the height of the arch openings of the nave arcade should be taller than the height of the columns by half of the column height. Consequently, the arch's height is one and a half times the column's height, and their ratio is 3:2.
Because the spacing of the columns determines the height of the round arches and this dimension is less than half the column height, it was necessary to add space between the columns and the arches in order to maintain this whole-number ratio. Along the outer wall, this space is detailed as an entablature, and along the nave arcade, the gap between the columns and bases of the nave arches is filled by impost blocks composed of sections of an entablature.
The use of extra moldings at the tops of capitals had precedents in Byzantine architecture. The proportionate size of the moldings at the top of the Byzantine capitals at San Marco, for instance, is greater than that of classical capitals, which generally abut the cornice without additional moldings.
The nave's low, wide proportions and classical vocabulary suggest that Brunelleschi's models were basilicas, both Roman and Early Christian, like the Basilica Ulpia, whose foundations remained, and St. Paul Outside the Walls, which is still intact.
The architectural forms stand out because there are no plaques or unnecessary relief sculptures. The ornamentation is provided by the detailing of the moldings and the crisp contrast created between the pietra serena and white stucco.
After the 1440s, arches along the outer walls were opened to form chapels. It is believed that Brunelleschi had wanted chapels along the nave, but he was forced to begin the nave without them because of patronage issues. The chapel project that was constructed was probably Michelozzo’s. Because the chapels displaced the windows that Brunelleschi originally designed, the Church's brightness was reduced.
The church of San Lorenzo was a parish church that was part of an Ambrosian monastery. It was supported by local families, and in the fifteenth century, was increasingly dominated by the Medici family, who paid much of the building cost. Over the next two centuries, the Medici commissioned a number of additions to the complex.
Contemporaneous with the rebuilding of the Church was the addition of a sacristy designed by Brunelleschi, located behind the left transept. It is called the "Old Sacristy," the Sagrestia Vecchia in Italian, to distinguish it from a second sacristy designed by Michelangelo a century later. This chapel is important as the first of many attempts by Renaissance architects to design a centralized space for worship.
In 1519, the Medici family commissioned Michelangelo to design a second sacristy, which was added behind the right transept arm. Called both the "New Sacristy" and the "Medici Chapel," it is similar to its predecessor in plan and use of materials but different in its two-part scheme of stone trim and its unusual combinations of architectural elements.
Soon after commissioning the Medici Chapel, the Medici family commissioned Michelangelo to design a library for the Medici collection of manuscripts and books, which were to be housed at San Lorenzo and opened to the public. A ground story vestibule contains stairs leading up to the second story reading room in which rows of crosswise desks stand beside corresponding lines of windows.
San Lorenzo's largest addition is the Cappella dei Principi (Chapel of the Princes), a new mortuary chapel that was begun by Ferdinando de' Medici, who wished to be buried there. It had been planned by his father, Cosimo I de' Medici, and was much larger than the sacristies designed by Brunelleschi and Michelangelo.
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