Dark earth is a thick, dark, urban sediment found between Roman and Medieval cultural layers of ancient urban settlements. Its study provides a means to understand early middle age societies and their relationship with urban spaces. The interpretation of these layers requires the use of detailed analysis primarily found within the discipline of Geoarchaeology. For this thesis, 20 stratigraphical layers (taken from Beauvais, Metz and Noyon) have been studied using geoarchaeological methods of analysis. Their study is based on an inventory of observations on dark earth compiled from five regions in the north of France (Haute -Normandie, Picardie, Île-de-France, Champagne-Ardenne and Lorraine). The research contained here demonstrates the high potential for the information contained within dark earth. Stratigraphical and latent feature analysis confirms the complexity of dark earth organisation. The physico-chemical characterisation of 89 stratigraphical units and the micromorphological analysis of 79 thin sections has both enabled the identification of the processes which led to the formation of dark earth and suggests the activities and urban, socio-spacial, practices which created them. This work also demonstrates the diversity of the material from which dark earth originates. This material is often in the form of small, regular, mixed deposits, and result from wastes from numerous activities, be they domestic or artisanal, or from re-reworked interior or external spaces. This research therefore brings substantial new information to the study of urban spaces between the Roman and Medieval periods and proposes an approach and ways of working in order to analyse the complexity of these spaces.