Two polished stone balls shaped about 5,500 years ago — linked to a mysterious practice almost unique to Neolithic Britain — have been discovered in an ancient tomb on the island of Sanday, in the Orkney Islands north of mainland Scotland. Early researchers suggested that the balls were used as weapons, and so they were sometimes called "mace heads" as a result. Another idea is that rope could have been wound around the lobes carved into some of the balls to throw them. But most archaeologists now think the stone balls were made mainly for artistic purposes, perhaps to signify a person's status in their community or to commemorate an important phase of their lives, said archaeologist Vicki Cummings of the University of Central Lancashire in England, who led the excavations of the tomb on Sanday.