A bio-archaeologist with the University of Reading, in the U.K., has found an ancient dog’s red-painted penis bone along with a trove of other bones, in an ancient Roman era quarry shaft. In her paper published in the Oxford Journal of Archaeology, Ellen Green describes where the bone was found, its condition, and possible reasons for it being painted red.

In her paper, Green notes that in 2015, a group of archaeologists digging at a site called Nescot, located near the modern town of Ewell, came upon a 4-meter-deep shaft that had been dug into the rock. Subsequent work revealed that the shaft had been used as a grave of sorts; it held hundreds of human and animal bones. In this new effort, Green focuses her efforts on one particular bone—a canine baculum (penis bone) that had been painted using red ochre.

Green notes that the remains of more than 280 domestic animals had been found in the shaft, 70% of which were dogs. None showed signs of butchering, disease or burning, which suggested they had been pets or working animals that had died and were buried. Just one of the canine baculum had been painted, making it stand out.

Green states that during Roman times, the penis, or depictions of it, were used in many contexts, many of which involved hoping for good luck. She suspects that the bone from the shaft likely played a role in a ritual of some sort, either before being tossed into the quarry shaft, or during its internment. She notes that other objects found in the shaft support the idea that the bone could have played a role in a larger ritual—perhaps one related to fertility.