WASHINGTON: The ancient ritual meaning of Stonehenge is still a mystery, but researchers are one step closer to understanding how the famous stone circle was created. The unique stone lying flat at the center of the monument was brought to the site in southern England from near the tip of northeast Scotland, in the journal Nature. It’s not clear whether the 16-foot (5-meter) stone was carried by boat or across land — a journey of more than 460 miles (740 kilometers). “It’s a surprise that it’s come from so far away,” said University of Exeter archaeologist Susan Greaney, who was not involved in the study. For more than a hundred years, scientists believed that Stonehenge’s central sandstone slab — long called the “altar stone” — came from much closer Wales. But a study last year by some of the same researchers showed that the stone didn’t match the geology of Wales’ sandstone formations.