The chapel is in the form of a parallelogram, three sides of which are painted, the other being separated from the choir by a bronze gate of most exquisite workmanship, designed by Ghiberti, or, as others say, by Brunelleschi, and executed partly by Simone Donatello.

On the wall, to the left as we enter, is a series of subjects from the Life of the Virgin, beginning, as usual, with the Rejection of Joachim from the temple, and ending with the Nativity of our Saviour.

The end of the chapel is filled up by the Assumption of the Virgin, the tomb being seen below, surrounded by the apostles; and above it the Virgin, as she floats into heaven, is in the act of loosening her girdle, which St. Thomas, devoutly kneeling, stretches out his arms to receive.  Above this, a circular window exhibits, in stained glass, the Coronation of the Virgin, surrounded by a glory of angels.

On the third wall to the right we have the subsequent History of the Girdle, in six compartments.

St. Thomas, on the eve of his departure to fulfil his mission as apostle in the far East, intrusts the precious girdle to the care of one of his disciples, who receives it from his hands in an ecstasy of amazement and devotion.

The deposit remains, for a thousand years, shrouded from the eyes of the profane; and the next scene shows us the manner in which it reached the city of Prato.  A certain Michael of the Dogomari family in Prato, joined, with a party of his young townsmen, the crusade in 1096.  But, instead of returning to his native country after the war was over, this same Michael took up the trade of a merchant, travelling from land to land in pursuit of gain, until he came to the city of Jerusalem, and lodged in the house of a Greek priest, to whom the custody of the sacred relic had descended from a long line of ancestry; and this priest, according to the custom of the oriental church, was married, and had “one fair daughter, and no more, the which he loved passing well,” so well, that he had intrusted to her care the venerable girdle.  Now it chanced that Michael, lodging in the same house, became enamoured of the maiden, and not being able to obtain the consent of her father to their marriage, he had recourse to the mother, who, moved by the tears and entreaties of the daughter, not only permitted their union, but bestowed on her the girdle as a dowry, and assisted the young lovers in their flight.

In accordance with this story, we have, in the third compartment, the Marriage of Michael with the Eastern Maiden, and then the Voyage from the Holy Land to the Shores of Tuscany.  On the deck of the vessel, and at the foot of the mast, is placed the casket containing the relic, to which the mariners attribute their prosperous voyage to the shores of Italy.  Then Michael is seen disembarking at Pisa, and, with his casket reverently carried in his hands, he reenters the paternal mansion in the city of Prato.