In Celtic, dol means, “table.” A dolmen is a tomb made of three enormous stones known as megaliths. Two vertical megaliths support a third megalith, which rests flat like a tabletop, essentially mirroring the post-and-lintel system. Dolmens are usually built into a mound of earth, forming an interior burial chamber big enough to hold a single body. Dolmens were later used as passage entryways into larger structures.