Erich Mendelsohn's Einstein Tower is the purest building of a counter-current — Expressionism — against modern architecture's obsession with the right angle and the flat surface. Here the building is designed not as an assembly of separate parts (wall, roof, window) but as a fluid sculpture moulded in a single gesture.

The building houses a solar telescope and a laboratory to test Einstein's theory of relativity; Mendelsohn wanted to cast the dynamism of this scientific programme into form. The mass curves as if shaped by hand from a soft material: windows turn flowing around corners, surfaces join one another without sharp joints, stairs and exits bud organically from the body. Mendelsohn in fact designed the whole structure to be cast in reinforced concrete as a single fluid shell — the nature of concrete, poured into formwork and able to take any shape, was ideal for this plastic language.

But the timing met the material shortage of post-war Germany; when concrete formwork proved too costly, much of the building was raised in brick and coated with thick render to imitate that fluid concrete look. This creates an interesting tension between form and material: the eye sees the plasticity of concrete, but beneath it is brick. The Einstein Tower is a manifesto showing that architecture can think not only in the straight line but in continuous curve and moulded mass — an early declaration of the formal freedom of reinforced concrete.