A dolmen is a type of single-chamber megalithic tomb, usually consisting of two or more vertical megaliths supporting a large flat horizontal capstone. Most date from the early Neolithic (4000–3000 BC) and were sometimes covered with earth or smaller stones to form a tumulus. Small pad-stones may be wedged between the cap and supporting stones to achieve a level appearance. It remains unclear when, why and by whom the earliest dolmens were made. The oldest known are found in Western Europe, dating from 7,000 years ago. They are regarded as tombs or burial chambers, despite the absence of clear evidence for this. Image taken from Primitive Man by Louis Figuier, 1870 (cropped and cleaned).