Kinetic architecture is a concept through which buildings are designed to allow parts of the structure to move, without reducing overall structural integrity. A building's capability for motion can be used just to: enhance its aesthetic qualities; respond to environmental conditions; and/or, perform functions that would be impossible for a static structure. The possibilities for practical implementations of kinetic architecture increased sharply in the late 20th century due to advances in mechanics, electronics, and robotics. History Rudimentary forms of kinetic architecture such as the drawbridge can be traced back to the Middle Ages or earlier. Yet it was only in the early 20th century that architects began to widely discuss the possibility for movement to be enabled for a significant portion of a buildings' superstructure. In the first third of the 20th century, interest in kinetic architect was one of the stands of thought emerging from the Futurism movement. Various papers and books included plans and drawings for moving buildings, a notable example being Chernikhov's 101 Architectural Fantasies (1933). For the first few decades of the 20th century kinetic architecture was almost entirely theoretical, but by the 1940s innovators such as Buckminster Fuller began experimenting with concrete implementations, though his early efforts in this direction are not regarded as totally successful. In 1970, engineer/architect William Zuk published the book Kinetic architecture, which helped inspire a new generation of architects to design an increasingly wide range of actual working kinetic buildings. Assisted by new concepts such as Fuller's Tensegrity and by developments in robotics, kinetic buildings have become increasingly common worldwide since the 1980s. Themes By the early 21st century three interrelated themes had emerged. The first is for functional buildings such as bridges which can elevate their midsections to allow tall ships to pass, or stadiums with retractable roofs such as the Veltins-Arena, Millennium Stadium in Cardiff, or Wembley Stadium. A second theme is for fantastic structures that can perform Transformer style changes of shape or which have a visually stunning appearance. The bird-like Burke Brise soleil at the Milwaukee Art Museum is a well regarded example of this, though it also has a functional aspect in that its movement allows it to shade the crowds from the sun or protect them from storms. The third theme is for movement to occur on the surface of the building, creating what Buckminster Fuller called a "skin-like articulation" effect. A classic example