A dolmen, also known as a portal tomb, portal grave, or quoit, is a type of single-chamber megalithic tomb, usually consisting of three or more upright stones supporting a large flat horizontal capstone. Most date from the early Neolithic period (4000 to 3000 BC). Dolmens were usually covered with earth or smaller stones to form a barrow, though in many cases that covering has weathered away, leaving only the stone "skeleton" of the burial mound intact.
Stonehenge-like structure found on sonar at the bottom of Lake Michigan! Researchers looking for shipwrecks at Lake Michigan found ancient Stonehenge-like structure 40ft beneath the waters surface! This could be as much as 10,000 yrs. old.