The rising late summer sun cuts through the morning fog on the green expanse of Salisbury Plain in Wiltshire, England. The rays slice across a towering circle of expertly carved stone slabs, casting long shadows. A handful of men gather at the center of the prehistoric megalithic structure, their eyes on the 16-foot-long stone lying at the monument’s heart, the Altar Stone. Like many of Stonehenge’s visitors, the men—researchers from as far as Australia—traveled here to marvel at the size and significance of the monument, which was built about 4,500…