The chapel which opens at the beginning of the right transept of the cathedral is the most important Marian shrine in Siena; it holds the image of Most Holy Mary of Grace Advocate of the Sienese, the work of the painter Dietisalvi di Speme and better known as the Madonna del Voto (“The Madonna of the Vow”). For centuries the Sienese have turned to her in moments of trial, whether personal or communal, as the numerous ex votos hanging on the walls of the chapel bear witness, donated to the Virgin by the faithful as a sign of thanksgiving.
According to tradition, the people of Siena made a vow in front of this painting, consecrating the city to Siena on the eve of the battle of Montaperti (1260), when the Sienese defeated the superior Florentine troops, bringing the city to its highest moment of splendor. In reality, the vow was made in front of another painting, showing the Virgin and Child enthroned, known as the Madonna of the Big Eyes, one of the earliest paintings of the Sienese school, painted in the second quarter of the thirteenth century by the Master of Tressa and now kept in the Museo dell’Opera.
The Madonna of the Vow was commissioned to Dietisalvi di Speme precisely as a result of the Sienese victory at Montaperti and is usually dated around 1270. Originally placed on an altar in the right aisle of the cathedral, the image soon became the object of great veneration, so much so that around the middle of the fifteenth century, at the initiative of the Sienese government and with public financing, it was decided to build a chapel, called the Chapel of Graces (or of Thanksgiving), to give the painting a more suitable setting. In the second half of the seventeenth century, this chapel was dismantled and Pope Alexander VII, born Fabio Chigi of Siena, decided to erect the current chapel, entrusting the work to the great baroque artist Gian Lorenzo Bernini. This same desire to give the image of Our Lady a more noble setting is a tangible sign of the profound, constant devotion of the Sienese to the Virgin Mary.
Bernini designed a sumptuous round room characterized by a great profusion of marble. The fulcrum is the altar: in the center, held up by bronze gilt angels who stand out against a lapis lazuli blue background, the color that manifests divinity, is the Madonna of the Vow. The painting, still reflecting the Byzantine style, shows the Virgin holding the Child in her arms, her eyes veiled with sadness in knowledge of the Passion her son will undergo. Jesus is shown giving his blessing, holding the scroll of the Holy Scriptures, emblem of knowledge, in his hand.
Four niches are set into the chapel walls, each one holding a statue: on either side of the altar are Saint Bernardino and Saint Catherine of Siena, the city’s two great saints, sculpted by Antonio Raggi and Ercole Ferrata respectively, in 1662; in the other two niches are Saint Mary Magdalene and Saint Jerome, masterpieces by Bernini, both of them exemplifying penitence and every Christian’s need for conversion to the Kingdom of God.
Above the statues are four marble bas-reliefs illustrating Episodes in the Life of the Virgin: her Birth, Presentation in the Temple, Visitation, and Dormition. Made by various sculptors of the Roman school, they reiterate the centrality of the figure of Mary in the chapel.
On the walls, too, are a canvas by Carlo Maratta presenting again the subject of the Visitation, and a late eighteenth-century mosaic of The Flight into Egypt, replacing a canvas by Maratta that had deteriorated.
In front of the altar, finally, is an elegant sculpture by Antonio Viligiardi (1918) representing Gratitude, embodied by the young girl offering a votive lamp to Mary.