They are Roman burials in the form of underground passages in which the dead were buried or their bones were kept. The bodies of some monks are also preserved with their daily clothes and sometimes with ropes that they wore as penance. The corpses are dried on ceramic racks and then washed with vinegar. These vaults were sometimes also used as shelters and hideouts in wars. The history of these catacombs in Palermo dates back to the sixteenth century, when Silvestro of Gubbio was embalmed in 1599 AD.