Researchers studying the archaeological site at Göbekli Tepe have uncovered the remains of human skulls that have had long grooves deliberately carved into them. The carved skull fragments, belonging to three different individuals, are amongst the remains of hundreds of other skull remains found amongst the site’s ancient T-shaped limestone monoliths, prompting the researchers to believe that Göbekli Tepe may have been home to one of the world’s first skull cults.

The grooves on the skull fragments, along with a small hole bored into one of the pieces, were found to have been deliberately carved using stone tools, and not caused by the claws of animals. The grooves are between 0.2 and 4 millimeters deep, and were made shortly after the individuals’ deaths, as there is no additional bone growth to indicate the individuals had healed after the grooves were cut, and the marks were made while the bone was still fresh and elastic, before it had a chance to decay.

Although no evidence of human burial has been found at Göbekli Tepe, the research team believes the grooves in question were used to hold cords in place that would attach the skulls to the top of a pole, or possibly suspended from a cord that was attached through the bore-hole in the one skull exhibiting that feature. The research team was unable to properly determine the age of the skull fragments, but Göbekli Tepe itself has been definitively dated to have been in use between 11,500 and 9,000 years ago.