For a full thousand years before the conquest, peoples of the Pueblo area of the American Southwest manipulated adobe clay to meet their architectural needs with marked cleverness and skill. In the dim beginning, they used it to stop the cracks of their slab-lined storage cists against rodents and trickling sand. Later, they applied stout crusts of it over the thatch that covered the pole walls and roofs of their singleroomed dwellings. Later still, they learned to make independent walls of it. Usually these were built up layer by layer much as were pottery vessels of the day. But occasionally they were made of “turtlebacks,” which, though of pure clay in rare instances, customarily'consisted of a core of twigs or other vegetation encased in mud. At their architectural zenith, the Pueblo raised massive adobe structures of pise-like appearance in localities where good stone was absent or hard to obtain and used it universally for mortar in stone construction, as well as for floors, plaster and roof covering.