The chapel, created by taking over the front part of the old sacristy, was ordered built by Niccolò Bensi in 1466 to hold the sacred head of Saint Catherine, the most important and valuable of her relics, which was brought to Siena after her death.
Catherine died in Rome on 29 April 1380 and was buried in the cemetery of Santa Maria sopra Minerva, but soon afterwards, because the cemetery was so damp, her body was exhumed and buried inside the church itself. On this occasion, Raymond of Capua, at the time General of the Dominican Order, asked and obtained from Pope Urban VI permission to detach the head from the body. The sacred relic was secretly taken to Siena in a silk bag which is still preserved in the Shrine of her house.
In 1385 Raymond informed the Consistory of the Republic of Siena that Catherine’s head was in Siena. Thus a solemn procession was organized, starting from the church of San Lazzaro outside Porta Romana, and moving towards the Basilica of San Domenico, where the relic was placed, enclosed in the copper bust which is now kept in the case to the right of the entrance into the chapel.
After Catherine’s canonization on 29 June 1461 by Pope Pius II, Niccolò Bensi, a member of a Sienese family, decided to have this chapel built to give the precious relic a worthy setting. The beautiful marble altar in the center of the back wall was carved in 1466 by Giovanni di Stefano, also commissioned by Bensi, as the inscription running along the base tells us. The sacred head is inside the central niche, protected by a gold grille. The copper bust which contained it earlier was replaced by one made of silver, designed by Giovanni di Stefano, and then in 1711 by an urn made by Giovanni Piamontini (now kept in a chapel in the right transept), where the relic stayed until 1931, when the Dominicans decided to place it in the current urn made of silver and enamels in the form of a Gothic church by the Florentine goldsmith David Manetti according to a design by the silversmith Angelo Giorgi.
In the course of the centuries, the sacred relic has been involved in various tumultuous events, but has always remained intact. In 1531 it risked destruction by a violent fire that broke out in the Basilica, but one of the friars, Guglielmo da Firenze, rushed into the flames and carried the relic out to safety. In May 1609, after a procession, the inhabitants of the Fontebranda district attempted to seize it so as to keep it definitively in their neighborhood; riots broke out for several hours, until the Collegio di Balìa (the highest local authority) intervened and had the sacred head brought back to San Domenico. Almost two centuries later, in 1798, the relic remained surprisingly untouched by an earthquake which damaged the Basilica; moved to the Cathedral and placed inside the Piccolomini Library, it was brought back to its proper place on the first Sunday after Easter in 1806.
A few decades after the construction of the chapel and its marble altar, the painted decoration of the walls was begun. In 1526 the artist Giovanni Antonio Bazzi, known as Sodoma, painted to the sides of the altar two of his most celebrated masterworks, The Mystical Trance of Saint Catherine and The Ecstasy of Saint Catherine, which bear witness to the intensity with which Saint Catherine prayed. Her trance was not a matter of ‘sentimental’ excess, but of losing consciousness in the face of the greatness of God’s love. Her ecstasy was a consequence of being completely absorbed by contemplation of God, so much so that it is also called spiritual rapture. Despite the limited wall surface available to him, the artist succeeded in given these scenes an extraordinary monumentality, joining to the perfection of the drawing and the masterful combination of colors a solemn, measured compositional structure. Sodoma also painted the large, crowded fresco of The Beheading of Niccolò di Tuldo. This episode is narrated in one of the most meaningful pages of the Epistolary. In 1377 Niccolò di Tuldo, a gentleman from Perugia, was unjustly sentenced to death by the Sienese magistrates for spying. While he was in prison, he fell into a state of profound desperation. Saint Catherine came to visit him and comforted him with her words to the point that he managed to submit his will to the divine plan, letting himself be led to the scaffold “like a meek lamb.”
The painting on the opposite wall was done in oils on the wall surface by another great Sienese painter, Francesco Vanni, between 1593 and 1596. The scene, set on a columned porch, shows Saint Catherine Freeing a Woman from Possession by a Devil amid the wonderment of a mixed crowd of bystanders made up of noblemen, religious, beggars and ordinary people, underscoring the universal nature of the Saint’s message.
The chapel is completed by a very fine fifteenth-century inlaid marble floor illustrating Orpheus and the Animals, designed by an artist whose manner is close to Francesco Giorgio Martini.