Thigh and shin bones
The walls are made of thigh and shin bones with fragments of skull bones shoved in between.
“On archaeologically examined graveyards we often see large pits [or] layers with lots of loose human bones, from clearing older graves, but we have never seen structures like walls, which are intentionally built with human bones,” lead researcher Janiek De Gryse told IFLScience.
Gryse also added that the structures were likely built from the middle of the 12th-century until 1784 as overflow from the church's cemetery. He explained that bones played an important role during those days.
“Given that the faithful believed in a resurrection of the body, the bones were considered the most important part. That is why stone houses were sometimes built against the walls of city graveyards to house skulls and the long bones in what is called an ossuary,” said De Gryse.
When cemeteries got too full, bones were often exhumed to make space for the newly-deceased. In those cases, the larger bones were usually collected leaving behind the smaller pieces.
“In the case of the ‘bone-walls’ of Ghent, there is an extra dimension to it. The bones from the upper limbs are absent; the walls consist only of bones from the lower limbs,” said Gryse.
“At the moment we are still examining which idea caused this. Is it only a practical thing (piling up bones in a very compact way) or is there also a religious [or] spiritual dimension?”
The researchers have radiocarbon-dated the bones and found that most of the material is from the second half of the 15th-century. Whatever the reason for the structure, we can all agree it is a pretty disturbing construction.