Archaeologists digging underneath a Cathedral in Belgium were met with a horrifying sight after recently discovering walls made entirely out of human bones and shattered skulls.

While unsure of their exact origin, the research team working at Saint-Bavo's Cathedral in Ghent believes that the bones were moved from the graveyard outside the church at a time when the cemetery was being cleared.

Project leader Janiek De Grysed said: "When clearing a churchyard, the skeletons cannot just be thrown away. 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 or a bone house."

De Grysed also noted that the walls would not be opened up to the public as a tourist attraction, but would instead be removed for further inspection. "There's a great deal of research still to be done," he added. 

The bones found were all from the thigh, shin and skull - supposedly because they were cleared in a hurry and small fragments would be harder to locate.

A newsletter from archaeologist Ruben Willaert explained more:

"When clearing graves, people often hurried and did not bother collecting smaller or fragile bones such as vertebrae, ribs, bones from hands and feet. So a selection of skulls and long bones emerged," it read.

The newsletter added that none of the bones in the structure belonged to kids, because children's bones "are small and fragile".

"Children's graves generally received less care and attention than the adult graves," it added.