A dolmen 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 early Neolithic (4000–3000 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.

Dolmen - Wikipedia