On the night of August 14, 1730, thieves stole the ciborium containing 351 consecrated hosts from the tabernacle of the Basilica of San Francesco in Siena. Three days later, on the feast of the Assumption, a priest at the nearby Church of Santa Maria di Provenzano discovered the hosts in the alms box, soiled but intact.
They were brought back to San Francesco with great solemnity and — rather than being consumed, as the Church's discipline normally required — were placed in a new ciborium for veneration. They were expected to deteriorate within weeks.
Instead, they have remained perfectly preserved for nearly three centuries. Multiple scientific examinations, beginning with one ordered by Archbishop Tiberio Borghese in 1789 and continuing through the 20th century, have found no preservatives and no decay. The most recent (1914, with subsequent monitoring) confirmed that the hosts remain fragrant and intact, contrary to every known law of biology.
Pope St. John Paul II visited the basilica in 1980. Looking upon the relic, he exclaimed simply: 'Here is the Presence!'