A rough brick anti-facade and undistinguished stony bulk hide what is most likely the oldest church in Florence, founded in a.d. 393. It was later the Medici family’s parish church, and Cosimo il Vecchio, whose wise behind-the-scenes rule made him popular with the Florentines, is buried in front of the high altar. The plaque marking the spot is inscribed pater patrie—“Father of His Homeland.”

Off the left transept is the Sagrestia Vecchia (Old Sacristy), one of Brunelleschi’s purest pieces of early Renaissance architecture. The focal sarcophagus contains Cosimo il Vecchio’s parents, Giovanni di Bicci de’ Medici and his wife, Piccarda Bueri, and a side chapel is decorated with an early star map that shows the night sky above the city in the 1440s (a scene that also features, curiously, in Brunelleschi’s Pazzi Chapel, in Santa Croce). On the wall of the left aisle is Bronzino’s huge fresco of the “Martyrdom of San Lorenzo”; the poor soul was roasted on a grill in Rome.

Left of the church’s main door is an entrance to the cloister and inside it a stairwell leading up to the Biblioteca Laurenziana (Laurentian Library). Michelangelo designed this library in 1524 to house the Medici’s manuscript collection, and it stands as one of the most brilliant works of Mannerist architecture.