The second Eucharistic miracle of Siena has roots in the 13th century when special services and festivities were introduced in honor of the feast of the Assumption of the Blessed Virgin Mary. These observances became traditional and were still conducted at the time of the miracle. So it was that on August 14, 1730, during devotions for the vigil of the feast, while most of the Sienese population and the clergy of the city were attending these services, thieves entered the deserted Church of St. Francis. Taking advantage of the friars' absence, they made for the chapel where the Blessed Sacrament was kept, picked the lock to the tabernacle and carried away the golden ciborium containing consecrated Hosts.
The theft went undiscovered until the next morning, when the priest opened the tabernacle at the Communion of the Mass. Then later, when a parishioner found the lid of the ciborium lying in the street, the suspicion of sacrilege was confirmed. The anguish of the parishioners forced the cancellation of the traditional festivities for the feast of Our Lady's Assumption. The Archbishop ordered public prayers of reparation, while the civil authorities began a search for the consecrated Hosts and for the scoundrel who had taken them.
Two days later, on August 17, while praying in the Church of St. Mary of Provenzano, a priest's attention was directed to something white protruding from the offering box attached to his prie dieu. Realizing that it was a Host, he informed the other priests of the church, who in turn notified the Archbishop and the friars of the Church of St. Francis.