A strange custom developed in the 18th century whereby the skulls of the dead were placed in St. Michael's chapel, often decorated with wreaths of ivy or garlands of roses, black crosses, and the owners' names, professions, and death dates. One skull has a serpent winding itself through the previous owner's eye cavaties and this is said to represent the cause of his death. An assortment of these neatly stacked skulls can be seen in the chapel for a small admission charge.
This practice was officiallly stopped in the 1960s, about the time the Catholic Church began permitting cremation, although the 'youngest skull' is from 1983.
Was googling these skulls when I came across this image, I love the way the shapes accentuate the skulls shape and gothic lettering on them, very good picture!