A dolmen (ˈdɒlmɛn) or portal tomb is a type of single-chamber megalithic tomb, usually consisting of two or more upright megaliths supporting a large flat horizontal capstone or "table". Most date from the Late Neolithic period (40003000 BCE) and were sometimes covered with earth or smaller stones to form a tumulus (burial mound). Small pad-stones may be wedged between the cap and supporting stones to achieve a level appearance. In many instances, the covering has eroded away, leaving only the stone "skeleton". The Korean Peninsula is home to the world's highest concentration of dolmens, including "cemeteries" consisting of 30–100 examples located in close proximity to each other; with over 35,000 dolmens, Korea alone (for unknown reasons) accounts for approximately 40% of the global total. It remains unclear when, why and by whom the earliest dolmens were made. The oldest known are found in Western Europe, dating from c. 7,000 years ago. Archaeologists still do not know who erected these dolmens, which makes it difficult to know why they did it. They are generally all regarded as tombs or burial chambers, despite the absence of clear evidence for this. Human remains, sometimes accompanied by artefacts, have been found in or close to the dolmens which could be scientifically dated using radiocarbon dating. However, it has been impossible to prove that these remains date from the time when the stones were originally set in place. The word dolmen entered archaeology when Théophile Corret de la Tour d'Auvergne used it to describe megalithic tombs in his Origines gauloises (1796) using the spelling dolmin (the current spelling was introduced about a decade later and had become standard in French by about 1885). The Oxford English Dictionary does not mention dolmin in English and gives its first citation for dolmen from a book on Brittany in 1859, describing the word as "The French term, used by some English authors, for a cromlech ...".