The vaulted cellar of the flour building of Cluny Abbey offers a fine example of cross-ribbed vaults. This early 12th-century invention revolutionized architecture by freeing load-bearing walls and allowing large windows to be opened to let light into the buildings. Contrary to the single-block Romanesque vaults resting on load-bearing walls, the cross-ribbed vaults do not rest directly on the walls but on diagonally arranged arches (the ogives) which intersect on a key in the center and rest on the top of pillars. They thus make it possible to extend the span of the vault and channel the thrust towards points other than the load-bearing walls, hence paving the way to the Gothic style.