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 (table), although there are also more complex variants. 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.