This article presents a particular boundary object, the Barrage erected between 1966 and 1982 around the town of Djibouti. While it was meant to restrain immigration, the population of the town tripled. While it should have maintained French sovereignty, the territory became independent in 1977. Operated mostly by military forces, reinforced by a full set of physical, legal and ideological constraints, this wall represents an important exercise of coercion upon all the inhabitants. Out of its own reality, it produced different effects on society. From a presentation of the making and the evolution of this impressive boundary object, we propose different hypotheses about its role with respect to migration control and identity building. We conclude with some reflections about the place of the Barrage in the typology of boundaries and how it informs us about the function of contemporary walls.