Dolmen
A megalithic tomb chamber: upright slabs carrying a single capstone, once buried under a cairn.
The rules it illustrates
The chamber is as wide as the capstone is long. In a megalithic chamber the room can be no wider than the largest slab the builders can raise over it; the upright stones are set to suit the capstone, not the other way round.
Where it appears in the book
In the styles Prehistoric and Megalithic.
In the chapters Post and Lintel.