A dolmen (/'d?lm?n/) 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 (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".