In early history, man sought shelter in caves. The first step towards a freely designed dwelling – before the invention of the house – was the erection of a roof. For a long time, man reacted instinctively to his environment, internalizing the regional climatic conditions. That is why one finds similar built forms in similar environments around the world. The flat roofs of the Mediterranean and other areas with a comparable climate are accounted for by the hot summers and mild, snow-free winters of these regions. Roofs of that kind could never bear snow loads. During warm summer nights, the roofs also served – and still serve – as sleeping quarters, as a retreat from the daytime heat stored in the walls of the houses. The Hanging Gardens of Babylon, one of the Seven Wonders of the World, fascinated master builders for centuries and, especially in the Renaissance, inspired many imaginative designs. The garden began to liberate itself from the ground. Plants and pools of water were suddenly translated to the roofs of buildings. Man felt the urge to intervene in the natural order of things. (Thomas Wirth)