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.

It remains unclear when, why, and by whom the earliest dolmens were made. The oldest known dolmens are in Western Europe, where they were set in place around 7000 years ago, at the same time as the ancient civilisations of Egypt, India, and the Middle East.^{[citation needed]} Archaeologists still do not know who erected these dolmens, which makes it difficult to know why they did it. The most widely accepted theory^{[citation needed]} is that all dolmens are tombs or burial chambers. Human remains, sometimes accompanied by artifacts, have been found in or close to them, which could be scientifically dated. There is however no firm evidence that even this theory is correct. It has been impossible to prove that these archaeological remains date from the time when the stones were set in place.