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.[2]