It was either a miracle or perhaps just a legend: on July 6, 1484, an 8-year-old blond child with an angelic face was chasing an animal when he came to the gate of the Stinche prison, where he was blinded by a dazzling light: just at that moment he saw the image of the Virgin Mary detaching itself from the wall on which she had been painted and taking on human form. This event generated a very strong devotion, so much so that a few years later it was decided to build a church on that site. Once grown up and educated, that child became the eighth priest to be in charge of the basilica. The prison, a place of guilt and wretchedness, after the apparition became a place of faith and hope. The building was designed by Giuliano da Sangallo at the behest of Lorenzo de' Medici. It is considered an architectural masterpiece of the early Renaissance. The interior was built between 1486 and 1495, while the external facing was halted in 1506 and completed later.
Its Greek-cross plan with central dome is inspired by the Chapel by Filippo Brunelleschi. The low base on which the church rests and the external covering, incomplete, use the two colours of the alberese stone and green serpentine, traditionally employed to adorn different buildings in Prato and surrounding areas. Inside, the purity and simplicity of the relationship between the parts underscore the most complete Greek-cross plan temple in the Renaissance. The arms are decorated with four stained-glass windows made in 1491 to a design attributed to Domenico Ghirlandaio, depicting the Annunciation, the Nativity, the Assumption, and the Visitation. The altarpiece on the high altar preserves the miraculous 14th-century fresco, depicting Madonna with Child between Saints Leonard and Stephen, which was originally located on the external wall of the ancient 13th-century prison.