Situated adjacent to the Basilica di San Lorenzo in Florence, Italy, the Sagrestia Nuova forms an integral part of the museum complex known as the Medici Chapels.

It was thought to house the tombs of Pope Leo and, at the time, of Clement VII in the Sacristy, but the idea was soon abandoned in favor of the choir of San Lorenzo.

On 17 June, the artist sent a letter to Rome in which he wrote: "I work as hard as I can, and in fifteen days I'll get the other captain started, then I'll be left, of matters of importance, only and four figures.

Michelangelo, despite being linked to the Medici by working relationships since his youth, blatantly sided with the republican faction, actively participating, as person in charge of the fortifications, in the defense measures against the siege of the city in 1529–1530.

Clement VII's pardon was not long in coming, provided that the artist immediately resume work in San Lorenzo where, in addition to the Sacristy, the project for a monumental Laurentian Library had been added five years earlier.

It is clear how the pope was moved by the awareness of his not being able to renounce the only artist capable of giving shape to the dreams of glory of his dynasty, despite his ingratitude towards and betrayal of the Medici.

In that same period the artist was preparing two allegorical statues, the Heaven and the Earth, which were to have been sculpted by Niccolò Tribolo and placed in the niches on the sides of Giuliano's tomb; these however remained empty.

Although an entire wall with the tomb of the "Magnificent" was missing and the river deities, statues, stuccoes and frescoes required by the contract had yet to be created, the Sacristy was considered completed.

Particularly beautiful are the emblematic position of the Day, turned from the back which shows only the mysterious expression of the eyes in a barely sketched face, or the body of the Night which perfectly represents abandonment during sleep.

In the Renaissance, especially in environments influenced by the Florentine Neoplatonism of Marsilio Ficino, the Night rediscovers its attributes of Primordial Mother and is associated with the figure of Leda.

According to the doctrines of Orphism and Pythagoreanism, Leda and the Night are the personification of a double theory of death, according to which joy and pain coincide.

[5] As for the portraits of the dukes, Michelangelo sculpted them seated in two niches above their respective tombs, facing each other, both dressed as Roman leaders.

These sculptures, with attention to the smallest details, are idealized and do not reproduce real features, but nonetheless have a strong psychological character (Giuliano sitting in a proud posture with the baton of command is more haughtier and decisive, while Lorenzo, in a thoughtful pose, is more melancholic and meditative).

A popular tradition tells that someone criticized the lack of resemblance of the portrait to the true features of Giuliano; Michelangelo, aware that his work would be handed down over time, replied that in ten centuries no one would be able to notice.

[5] In a statement in the biography of Michelangelo that was published in 1553 by his disciple, Ascanio Condivi, and largely was based on Michelangelo's own recollections, Condivi gives the following description of the sculptures on the two Medici tombs: "The statues are four in number, placed in a sacristy... the sarcophagi are placed before the side walls, and on the lids of each there recline two big figures, larger than life, to wit, a man and a woman; they signify Day and Night and, in conjunction, Time which devours all things… And in order to signify Time he planned to make a mouse, having left a bit of marble upon the work (which [plan] he subsequently did not carry out because he was prevented by circumstances), because this little animal ceaselessly gnaws and consumes just as time devours everything”.

Speaking in the voice of the statue, it may contain a scathing critique of Cosimo I de' Medici's governance, according to Kenneth Gross:[13] Dawn is a sculpture by Michelangelo, executed for the chapel.

Against it is the sepulchre with the mortal remains of Lorenzo the Magnificent (died in 1492) and his brother Giuliano (killed during the Pazzi Conspiracy in 1478), surmounted by three sculptures.

[18][19] The three statues were later placed by Giorgio Vasari on a simple marble chest housing the remains of Lorenzo the Magnificent and his brother Giuliano de' Medici, for whom there was never the time to build a larger monumental tomb.