The owner boatmen of the River Seine travel wherever their professional activity takes them, over urban and suburban spaces. Can these boatmen be called suburban ? Their professional activity — and thus their residence defines a reticular space which is distinct from the type of space experienced by so-called "d’à terre" people. Located on the fringe of urban spaces, this reticular space can be called infra-urban or infra-suburban ; its exchanges with its surrounding spaces are scarce. The social life of these owner boatmen takes place in special urban centers, which are genuine "boatmen cities". These urban centers constitute alternative centralities. In addition, this atypical urban system, organized around the rivers, is totally disconnected from the dominant urban system. This paper aims at analyzing the uncommon urbanity of boatmen and the consequences of urban growth on their lives and spaces. Thus, the question of the place given to itinerant populations and to fringe areas will necessarily arise.