"Intervention in preexisting "historical" environment of urban centres in the way of rehabilitation, is a major problem both for the architects and for the theory of architecture. This paper attempts to discuss this problem through the presice data concerning the rehabilitation of a single house sited at Metaxourgion, besides the center of Athens. First, there is a reconstitution of the genealogy of this house, beginning from the very creation of its parcel, which faces a narrow street, itself created at the same time in the middle of a large plot divided in smaller lots. * Second, there is a confrotation between the actual situation of the social and built context and the real conditions of the architectural command. * Finally, there is an attempt to examine the principal ambiquities determining the nature of intervention vis a vis evolutionary process in the built environment: * On the one hand, the question of time. That is whether the building and the context analysis preceding intervention must be elaborated in the synchronical or the diachronical dimension. The analytical recording of the present and gen'erally visible situation of the builtscape is opposed to the reconstitution of its history which, although partially invisible, has certainly impregnated in a durable way both memories and forms. * On the other hand, the question of the whole. That is whether intervention in preexisting "historical" environmnet, generally considered like a complex petrifaction of all the contradictions which define the Ion gue durée of social life, must generate the evolution or the "achievement" of the builtscape. Otherwise, the urban collage and his reproduction by a kind of architectural bricolage is opposed to the rehabilitation of "coherences", whose projected whole has never had any real existence."