A relatively small building, Unity Temple, in Oak Park, Illinois, has assumed an importance in concrete history far beyond its size and appearance. In the words of Frank Lloyd Wright, this was "the first building in America to be cast complete, ornament and all, in forms--and to be let alone' as architecture' after the forms were removed." This bold leap forward helped free architectural concrete from the stigma of utilitarian construction.

Wright later described his concept: "Why not make wooden boxes or forms so the concrete could be cast in them as separate blocks and masses, these grouped about in an interior space in some such way as to preserve this sense of the interior space, the great room, in appearance of the whole building? And the block-masses might be left as themselves with no facing at all? That would be cheap and permanent and not ugly either. What roof? What had concrete to offer as a cover shelter? The concrete slab--of course. The reinforced slab. Nothing else if the building was to be thoroughbred, meaning built-in character out of one material...The flat slab was cheap and direct. It would be nobly simple. The wooden forms or molds in which concrete buildings must at that time be cast were always the chief item of expense, so to repeat the use of a single form as often as possible was necessary. Therefore a building square in plan. That would make their temple a cube--a noble form of masonry."

In 1971 Unity Temple was declared a National Historic Landmark.