Unity Temple in Oak Park, a national landmark (1908). Unity Temple was one of the first non-residential structures designed by Frank Lloyd Wright. Wright was a Unitarian, and agreed to help the Universalists construct a new church after their original one burned town in 1905. It was one of the first bipartite designs, where two sections of a building stand at different heights and are separated with a passageway. The lot for the Unity Temple was on a busy street, so Wright did not include any street-level windows. It's most important contribution, to architecture, however, may be its concrete exterior. Concrete was not viewed as a medium that could be useful in architecture, but it has since become the most important material and spawned the modernist movement.