In the 15th century, during the various phases of the Basilica’s reconstruction (including beneath the cloisters and rectory), a vast and well constructed underground area was discovered. This discovery required that most of the pre-existing architectural testimony be destroyed.

The crypts of the Laurentian Complex are most likely hiding ruins of the previous churches and of suburban buildings of Roman and medieval Florence. Some of these remains were discovered when Piazza San Lorenzo was leveled in 1912-1913. That’s when the present stairway to the Basilica substituted the bumpy terrain, which during medieval times, was called Monticulus Sancti Laurentii.

The underground chambers of the Laurentian Complex include the Medici burial crypt, to which we gain access from the entrance to the Museum of the Medici Chapels. This is where almost all of the tombs of the Medici family are located. Also located below the church is the undercroft, known better as the “Salone di Donatello”(only partially open during exhibitions). Here stand tombs of some illustrious individuals, beginning with Donatello and Cosimo il Vecchio. Finally, and most intriguing, are the walkways below the cloisters, from which open numerous rooms, now mainly turned into storage areas.

The area below the Parish was transformed into a cemetery for the Lorraine, by Emilio De Fabris at the end of the 19th century, in continuity with the area of Cosimo’s tomb. The tomb is visibly connected to the church by three iron gratings, facing the crypt of the Museum of the Medici Chapels.

Transformed into a cemetery from the 12th until the 18th century, the underground area of the Basilica was tidied up according to the wishes of the Elettrice Palatina in 1739-1742, when they assisted in the partial demolition of the preceding tombs and other modifications of the “Salone”. Once the reconstruction of Donatello’s tomb was completed, it was justly dedicated to the artist.

The cemetery premises which correspond to the side aisle to the right of the nave were allowed to be occupied already by the Medici princes of the three religious groups devoted to works of charity: the Holy Stigmata of St. Francis (located in the area below the New Sacristy), the SS. Sacramento (located in the area below the Old Sacristy), and del Sangue. They assembled together from the 16th century until 1785, when they were abolished by Pietro Leopoldo. Later, by the intercession of Ferdinando III of Lorraine, the two groups of the Stigmata and SS. Sacramento were once again united, enabling them to continue with their secular charity work.

The rooms that flank the underground walkways were connected to the senior canons’ living quarters. These rooms were utilized as storerooms and kitchens. After the drastic reduction of the number of canons that lived in the Complex, a large part of these storerooms were abandoned or turned into warehouses. During certain periods, outsiders were able to use parts of the warehouses. For example, they were used as a pantry for foodstuffs, thanks to the almost constant cool temperature, perfect for food preservation. During wartime, these rooms were utilized mainly as shelters to protect works of art.

During the 20th century the outer walkways below the cloisters were either blocked by new technical installations (hydraulic tubing, gas, and electrical lines...), or utilized as boxrooms. So much so that they were rendered practically unfit until the very recent interventions were reutilized, and still ongoing.