Carnac, on the coast of Brittany, is the densest megalithic alignment in the world, formed by more than three thousand standing stones (menhirs). There is no building here; yet Carnac belongs to the opening vocabulary of architecture, because it handles the most elementary structural element — the upright stone — with scale and order.

In the Ménec, Kermario, and Kerlescan groups, the menhirs are set in long parallel rows running roughly east-west; the Ménec alignment stretches some 1,165 metres with around 1,100 stones. The stones are not placed at random but graded by size: giants over four metres at one end, diminishing blocks as the rows proceed. This stepping shows the array was subject to a deliberate visual and spatial order.

Architecturally, Carnac documents two kinds of knowledge. The first is material and labour logistics: local granite blocks quarried, transported, and raised upright by hand. The second, and more important, is the idea of alignment — the spacing, registration, and orientation of the stones is among the earliest large-scale instances of space ordered by human hand. There is as yet no wall, roof, or enclosed volume; but notions such as "row," "axis," and "proportion" rehearse themselves here in the open air. Carnac thus represents the face of architecture that precedes enclosed space — the ordering of the landscape itself.