The Medici Chapels (Cappelle medicee) are two structures at the Basilica of San Lorenzo, Florence, Italy, dating from the 16th and 17th centuries, and built as extensions to Brunelleschi's 15th-century church, with the purpose of celebrating the Medici family, patrons of the church and Grand Dukes of Tuscany. The Sagrestia Nuova, ("New Sacristy"), was designed by Michelangelo. The larger Cappella dei Principi, ("Chapel of the Princes"), though proposed in the 16th century, was not begun until the early 17th century, its design being a collaboration between the family and architects.
The Sagrestia Nuova was intended by Cardinal Giulio de' Medici and his cousin Pope Leo X as a mausoleum or mortuary chapel for members of the Medici family. It balances Brunelleschi's Sagrestia Vecchia, the "Old Sacristy" nestled between the left transept of San Lorenzo, with which it consciously competes, and shares its format of a cubical space surmounted by a dome, of gray pietra serena and whitewashed walls. It was the first essay in architecture (1521–24) of Michelangelo, who also designed its monuments dedicated to certain members of the Medici family, with sculptural figures of the four times of day that were destined to influence sculptural figures reclining on architraves for many generations to come. The Sagrestia Nuova was entered by a discreet entrance in a corner of San Lorenzo's right transept, now closed.
Though it was vaulted over by 1524, the ambitious projects of its sculpture and the intervention of events, such as the temporary exile of the Medici (1527), the death of Giulio, now Pope Clement VII and the permanent departure of Michelangelo for Rome in 1534, meant that Michelangelo never finished it. Though most of the statues had been carved by the time of Michelangelo's departure, they had not been put in place, being left in disarray across the chapel, and later installed by Niccolò Tribolo in 1545. By order of Cosimo I, Giorgio Vasari and Bartolomeo Ammannati finished the work by 1555.