The Basilica di San Lorenzo (Basilica of St Lawrence) is one of the largest churches of Florence, Italy, situated at the centre of the city’s main market district, and the burial place of all the principal members of the Medici family from Cosimo il Vecchio to Cosimo III. It is one of several churches that claim to be the oldest in Florence; when it was consecrated in 393 it stood outside the city walls. For three hundred years it was the city's cathedral before the official seat of the bishop was transferred to Santa Reparata. San Lorenzo was also the parish church of the Medici family. In 1419, Giovanni di Bicci de' Medici offered to finance a new church to replace the 11th-century Romanesque rebuilding. Filippo Brunelleschi, the leading Renaissance architect of the first half of the 15th century, was commissioned to design it, but the building, with alterations, was not completed until after his death. The church is part of a larger monastic complex that contains other important architectural works: the Old Sacristy by Brunelleschi; the Laurentian Library by Michelangelo; the New Sacristy based on Michelangelo's designs; and the Medici Chapels by Matteo Nigetti.
Though considered a milestone in the development of Renaissance architecture, S. Lorenzo has a complicated building history. Even though it was built – at least partially - under the direction of Filippo Brunelleschi, it is not purely of his design. The project was begun around 1419, but lack of funding slowed down the construction and forced changes to the original design. By the early 1440s, only the sacristy (now called the Old Sacristy) had been worked on as that and the church was being paid for by the Medici. In 1442, the Medici stepped in to take over financial responsibility of the church as well. Brunelleschi died, however, in 1446 and the job was handed over either to Antonio Manetti or to Michelozzo; scholars are not certain. Though the building was “completed” in 1459 in time for a visit to Florence by Pius II, the chapels along the right-hand aisles were still being built in the 1480s and 1490s.
By the time the building was done, many aspects of its layout, not to mention detailing, no longer corresponded to the original plan. The principal difference is that Brunelleschi had envisioned the chapels along the side aisles to be deeper, and to be much like the chapels in the transept, the only part of the building that is known to have been designed by Brunelleschi.
The most celebrated and grandest part of San Lorenzo are the Cappelle Medicee (Medici Chapels) in the apse. The Medici were still paying for it when the last member of the family, Anna Maria Luisa de' Medici, died in 1743. Almost fifty lesser members of the family are buried in the crypt. The final design (1603–1604) was by Bernardo Buontalenti, based on models of Alessandro Pieroni and Matteo Nigetti. Above is the Cappella dei Principi (Chapel of the Princes), a great but awkwardly domed octagonal hall where the grand dukes themselves are buried. The style shows Mannerist eccentricities in its unusual shape, broken cornices, and asymmetrically sized windows. In the interior, the ambitious decoration with colored marbles overwhelms the attempts at novel design (Wittkower, R. p. 126). At its centre was supposed to be the Holy Sepulchre itself, although attempts to buy and then steal it from Jerusalem failed.