Stone Age people would have encountered skulls on display or hanging from pillars at the site. German Archaeological Institute (DAI)

Archaeologists have discovered what seem to be the remains of a "skull cult" in an ancient ritual site in southeast Turkey.

More than 9,000 years ago — before the existence of the hanging gardens of Babylon, pyramids of Egypt, or Stonehenge — Neolithic, Stone Age people gathered at the site, called Göbekli Tepe.

No one is exactly sure why. But a new study published in the journal Science Advances by researchers from the German Archaeological Institute suggests that the location had some kind of ritualistic significance.

There is no sign that humans buried their dead there, but there are at least 691 shards and chunks of bone. At least 408 of those fragments come from human skulls.

The site also boasts monumental buildings with "monolithic T-shaped limestone pillars, an impressive repertoire of limestone sculptures, low and high reliefs," all in a prominent location, according to the study.

Decorative reliefs show the importance of the site. German Archaeological Institute (DAI)

In the study, the research team writes that skull fragments from at least three individuals show signs of deliberate modification.

Details of artificial skull modifications. A, C, and D are carvings; B is a drilled perforation. Julia Gresky, DAI

Deep grooves run across the forehead of some bones, going around the back of at least one. One skull has a hole drilled in it. None of these markings comes from decapitation or from taking the flesh and tissue off the bones, though other marks attest to this. Instead, they seem to have been inflicted shortly after death.

That indicates the skulls were somehow on display, perhaps even hung so that visitors would see them dangling.

Skull fragments with cut marks. German Archaeological Institute Similar remains have been found in other archaeological sites where there was some worship of skulls, including sites in ancient Anatolia and the Levant.

People have long venerated human skulls for several reasons — some worshipped ancestors, and others believed the dead could protect the living. Some groups also displayed the skulls of their enemies.

Anthropologists refer to these practices — where there seems to be religious or ritualistic practice and treatment done to skulls — as skull cults.

Researchers think early hunter-gatherers might have come together at the Göbekli Tepe site, which is home to one of the oldest known man-made buildings thought to have been constructed for prehistoric rituals.

This temple seems to have housed one of the oldest of these skull cults that researchers have encountered so far.