The Threshold Stone at Newgrange, a prehistoric passage tomb and ceremonial chamber dating from about 3200 BC. Boyne River Valley, County Meath, Ireland. Located directly in front of the entrance, the Threshold Stone is elaborately carved with spirals, concentric circles and diamond shapes. Their meaning is not known but theories are plentiful. Some believe that the three main spirals represent the tombs of Newgrange, Knowth and Dowth, with the wavy line below depicting the River Boine. Others think the three spirals represent life, death and eternity.