Charles Marville’s 425 photographs of Parisian streets and Ghémar Frères’ photographs of the banks of the Senne in Brussels are well known for their beauty, and are often associated with melancholy, or, on the contrary, with the recording of bad housing conditions. Both series were ordered by the cities between 1865 and 1867; both cities would destroy the subject of the photographs – the buildings – immediately thereafter. The question of the original purpose of the photographs has never been asked. A close reading of relevant documents makes clear that Marville’s photographs were meant to serve as tools for mapping medieval streets in the Topographie Historique. Probably influenced by Marville’s project, and with a remarkably similar relation to mapping and topography, Ghémar’s views of Brussels should be understood in the same context: as a contribution to the visual archive of the city itself.