The two monumental groups (for the tombs of Lorenzo, duke di Urbino, and Giuliano, duke de Nemours) are each composed of a seated armed figure in a niche, with an allegorical figure reclining on either side of the sarcophagus below. The seated figures, representing the two dukes, are not treated as portraits but as types. Lorenzo, whose face is shaded by a helmet, personifies the reflective man; Giuliano, who is holding the baton of an army commander, portrays the active man. At his feet recline the figures of “Night” and “Day.” “Night,” a giantess, is twisting in uneasy slumber; “Day,” a herculean figure, looks wrathfully over his shoulder. Just as imposing, but far less violent, are the two companion figures reclining between sleep and waking on the sarcophagus of Lorenzo. The male figure is known as “Dusk,” the female figure as “Dawn.”

Lorenzo the Magnificent (Medici, Lorenzo de') and his brother Giuliano the Elder were buried at the entrance wall, and over them was set up a marble group consisting of a “Madonna and Child” and the Medici patron saints Cosmas and Damian. The “Madonna” is a work of imposing majesty, completely by Michelangelo's own hand; the saints are the work of pupils after models by the master.