In the 18th century, while preparing for the Feast of the Assumption, there was a lot of Hosts preconsecrated for the celebration. Then, on the vigil of the Assumption, August 14, 1730, thieves broke into the Church of St. Francis, they picked the lock on the tabernacle and stole the golden ciborium which was filled with Hosts. Two days later at another parish a priest noticed something protruding from the offering box (poor box) which was only emptied about once per year. He opened the box and found someone had dumped the consecrated Hosts into it. Being that the box was not opened often, it had lots of dust and cobwebs in it - some of the Hosts were suspended in the cobwebs. The Hosts were compared to others at St. Francis and they were identical in size and iron marks from the baking process - these were indeed the stolen Hosts. The Hosts were put into another ciborium and not used, for they had been dirtied by the thief/thieves - but since they were consecrated, they were not destroyed.
"Okay," you say, "so where's the miracle?" Well, fifty years had passed and the Minister General of the Franciscan Order came to investigate - and not only had the Host not deteriorated in the least, upon tasting one he commented that it was fresh and incorrupt. They even had a pleasant smell. In 1789 the Archbishop of Sienna, with a number of other religious and dignitaries, had the Hosts examined under a microscope and further confirmed no sign of deterioration. Keep in mind, bread will start molding and deteriorating within days, or in best conditions (without freezing, which was not even plausible in the 18th century) a week or two. After more than fifty years, there should have been little resemblance to bread at all. What's more, is this miracle can be witness to this day!
I am also making this a short series on Eucharistic Miracles... stay tuned!