At Stonehenge each lintel is pegged to its uprights by a mortise-and-tenon joint and locked to its neighbours by tongue-and-groove joints, and each is curved to follow the circle: the joints of a timber frame reproduced in dressed sarsen.
The tops of the sarsen uprights carry projecting knobs (tenons) that fit hollows (mortises) cut into the undersides of the lintels, and the ends of adjacent lintels interlock. The lintels are gently curved on plan and the uprights taper and swell slightly, refinements that make the ring read as continuous from inside. The builders were evidently used to timber construction, and several earlier timber circles are known nearby, including at Durrington Walls.
The sarsens were worked with hammerstones, pounding the surface grain by grain. The heaviest uprights of the Great Trilithon weigh some thirty tonnes; the lintels, lifted more than four metres, around seven.
In a corbelled vault each course may project only a little beyond the one below, and each overhanging half must have its centre of gravity behind the inner face of its wall; load the tails of the stones with heavy hearting until the capstone is set.
stable if Σ W·x (behind the springing edge) > Σ W·x (in front)
A beam is squeezed along its top and stretched along its bottom; stone resists squeezing well but stretching badly, so a stone lintel must be deep in proportion to its span and cannot be long. Doubling the span quadruples the stress from its own weight.
σ ≈ ¾ ρ g L² ⁄ d (self-weight) · + ≈ 0.43 ρ g L³ ⁄ d² (a wall above)
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.
Build a round chamber of horizontal courses, each ring projecting a little beyond the one below, dress the inner face to a smooth curve, close the top with a capstone, and heap earth over the whole.
Build the circle of the living in timber, which decays, beside the settlement; build the circle of the ancestors in stone, which endures, apart from it; and join the two by avenues and the river.
Set up forked stakes, weave twigs between them and daub the walls with mud; roof them with reeds and leaves, steep enough to shed the rain.
Cite this page Chris Paton, “Joints of carpentry worked in stone”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/megalith-joinery. Text, drawings and models licensed under CC BY-NC 4.0.