The Sacred Belt in the Cathedral of Prato is a fine woolen green belt, brocade with some gold threads. A well-established tradition already at the end of the 13^th century identifies the relic of Prato with that which was donated by the Virgin, when she was assumed in Heaven, to St. Thomas. It is said that the relic came to Prato around 1141 thanks to the citizen Michele Dagomari, a pilgrim in the Holy Land who had it in the dowry, marrying in Jerusalem a maiden named Maria. Michele gave it to death (1172) at the parish priest of Santo Stefano where the Sacred Belt is still guarded.
The relic was the centerpiece of Prato religion and is considered a patrimony of the entire community: its public display from ancient times is governed by the statutes of the Commune, which carries a part of the keys necessary to extract it from its altar and reliquary.
The relic had been preserved, at least since the end of the 13^th century, near the main altar, hence with a sort of popular handshake (supported by the Commune), the relic was brought in 1346 near the church entrance and removed to the custody of the canons. The present Chapel was made in 1386-90 by Lorenzo di Filippo's project to give final settlement to the Sacred Belt. The interior space is entirely frescoed with Stories of the Virgin and the Sacred Belt, a cycle of astonishing figurative unit painted in 1392-95 by Agnolo Gaddi (1350-1396) and his workshop. In 1434-38 by Donatello and Michelozzo was realized the outside pulpit at the Cathedral for the Belt’s Display to the believers gathered in the square. Presently, the Display is made for Christmas, Easter, the 1^st of May, the 15^th of August, and in the most solemn way on the 8^th of September, in conjunction with the Historical Parade celebrations.