In the conclusion of his 1915 dissertation, the influential German urban planner Martin Wagner argued forcefully for a new approach to the role of green space in city planning. Referring to recent efforts to improve urban hygiene and general cleanliness in major German cities, especially the public bathhouse movement of the late nineteenth century, Wagner claimed that expansion and promotion of accessible green space constituted the next big challenge for those interested in improving urban living:
The health conditions of the big cities demand an expansion of sanitary living space. To incorporate nature into this development will be the communal-political challenge of the coming years. Cities, which encompass more than half of Germany's total population, have a duty . . . to secure the health of the German body and increase German strength. We must solve this challenge before we reach a point where a solution through natural means is no longer possible.