Science has shot down a lot of supposedly holy relics, proving them to be much younger than their claimed ages. Sometimes, however, it does the opposite, and new evidence has confirmed the age and function of a 13th-century sackcloth. The object in question has been associated with a saint even some atheists have a soft spot for – St Francis of Assisi.

According to legend, a sack filled with bread mysteriously appeared in the winter of 1224 on the doorstep of the Friary of Folloni, supposedly founded by St Francis two years before. Such aid would have been appreciated at any time, but the Friary was isolated by snow and wolves, and the friars were in danger of starving. How the sack could have been delivered under such conditions was hard to explain, so a story arose that angels provided a postal service from St Francis, who was at the court of Louis VIII of France. The sack was even marked with the lilies of the French court.

Naturally, many have been skeptical. There's no written evidence that the Friary even existed until a century later, and the era is notorious for fake relics. Apparently, the Friary used the sack's material as an altar cloth for centuries before having it preserved in 1732. Now science has confirmed some parts of the story.

Dr Kaare Lund Rasmussen, of the University of Southern Denmark, has reported in Radiocarbon that the sack dates to somewhere between 1220 and 1295, and is therefore not a later addition seeking to fleece pilgrims and tourists.

Moreover, Rasmussen found traces of ergosterol, a chemical produced by molds that used to be common on bread, suggesting that at some point the sack did indeed hold loaves. The timing of this is unknown, but it was presumably before food preservation methods started to be used.

One of the many legends surrounding St Francis, who the current Pope honored in choosing his name, is that in 1222 he sought to stay with the lord of the castle at Montella in southern Italy. Despite being well-known, Francis' fame had yet to reach the castellan, who, seeing his poverty, drove him from the castle. Francis took refuge in the Folloni forest, where he spent the night unhindered by the robbers and wolves often found there.

Moreover, while the rest of the forest was covered in a thick snow, the tree under which Francis and his companions lay was supposedly untouched, causing locals to request that he start a convent there.

Unfortunately, like the tale of an angelic postal service, this story cannot be tested by modern science.