The old Greeks gathered in front of a retaining wall on a hillside to practice early forms of democracy. However, through the ages of Babylonians, Romans and Chinese, the predominant purpose of the walls was security and defense - always as the construction of a peaceful inside versus a hostile outside. Only rarely has the historical justification for the construction of a wall been lost. Religious precincts required a clear geometrical demarcation, whereas the resistance against the eroding forces of the weather were fought against by a network of pragmatically placed stone walls in the land. For the longest time a city was unthinkable without - even defined by - the surrounding walls. It was these walls that guaranteed a different life: hence the meaning of city air makes you free. Retaining walls, fortifications and ramparts became the significant features of a landscape transformed by military engineering. Occasionally the protection by walls was one against the winds so that tempered courtyards would facilitate a better harvest. The dynamics of the industrial age demanded ever larger installations for energy generation: dams of unprecedented size have collected enormous quantities of water. Most present, however, are the walls as physical manifestations of socio-political intentions, visible symbols for separation.