Heavy, roughly rounded, ovular and oblong stones found at neolithic sites in the Sahara Desert, having a groove across the middle. From depictions in rock carvings, they are known to have served as anchors or drags for tethering ropes for domestic animals such as cattle, or for rope traps and snares for wild animals; the rope was wound or tied around the stone where the groove was and the weight of the stone kept the animal from running away.
