Introduction

In recent years, an increasing number of separation walls have been built around the world, and observers regularly voice worries about the current worldwide proliferation of walls. By and large, it is assumed that their presence fosters divisions and inequality. In particular, walls built in urban areas, where human density is higher and social diversity more accentuated, have exacted a heavy toll in terms of political divisions, ecological deterioration and human suffering. At the same time, however, homeless and displaced people, unprotected by any wall, are often terrorised by irregular militias, captured or evicted by state police, and have likewise endured terrible ordeals. As new types of walls, wall engineering, wall politics and wall cultures emerge, the wall increasingly becomes a multifaceted and enigmatic phenomenon. Urban walls and their effects seem to have become something that we need to investigate and analyse in a much more comprehensive and focused way than hitherto. In this introductory chapter, we introduce urban walls as a possible research field, and we suggest that the whole spatial functioning of walls can hardly be reduced to a black-and-white picture. Moving beyond simplistic interpretations, walls may instead provide an important case for the advancement of a general science of territories, or territoriology. Observing walls as basic territorialising devices has wide-ranging consequences. The ambivalence of walls rhymes with the territorial duality of protection and segregation; walls impact upon bodies and constrain circulations. But territoriology also suggests that there is more to walls than a two-dimensional effect. In fact, walls are always part of several overlapping processes of territorialisations, setting parameters of co-existence, both constraining and enabling meetings and flows.