This thesis attempts to understand the occupation regime of public space, by focusing on the place of the soldiers engaged in the Vigipirate plan and the Sentinelle operation. Starting from the assumption that soldiers patrolling in the urban public space are allogenous with the socio-spatial environment in which they intervene, we suggest that city-dwellers maintain with them a specific relation which could reveal their own way of being and doing with others through space. Individual spatialities (to put near or at a distance, physically or symbolically) and collectives games of places and placements both materialized this relationship between city-dwellers and the military. Those games of places and placements respond to logics of assignment/designation or self-assignment/self-designation to be or not in a given spot according to social position, spatial norms and emplacement. The personal lived tension of legitimation between the "what is" and "what should be" precisely expresses this regime of occupation of space. Moreover, the situations of interactions and perceived/lived co-presences between city-dwellers and the military are never identical and regular, therefore these games of place cannot be considered as occurring in a single dimension. The approach defended here will try to exhaust these mechanisms of places and placement by approaching different perspectives from which these places are apprehended by the actors : as soldiers in operation, as reservists in the Army, as city-dwellers. We intend to show that the occupied places and the held roles are not only multidimensional and constantly updated but are also to be understood as performative space always in tension.