Since the thirteenth century September 8th, the birthday of the Virgin, has been celebrated in Prato with the public display of her Holy Belt. In this paper I focus on the ceremony of the ostentation and its setting, the chapel built at the end of the fourteenth century and still in use. While seemingly a purely religious event, the ostentation evolved into a civic ritual imbued with political significance. The ceremony and its setting both reflected and shaped Prato's identity as guardian of the Sacred Belt by providing a focus for community pride and religious devotion, and by construction and sustaining social memory. At the same time, the mural decoration of the chapel, painted by the Florentine artist Agnolo Gaddi between 1392 and 1395, celebrated the civic identity of the commune while alluding to the political reality of Prato's absorption into the Florentine regional state.