Based on several case studies from Roman Italy (Ostia and Portus mainly), this presentation will demonstrate the importance to conduct interdisciplinary studies on the urban fabric of settlements located in river mouth environments. We will be particularly interested in showing the role of a geoarchaeological approach in these interdisciplinary researches. First, the urban fabric will be discussed following a planimetric approach. Reconstruction of the evolution of the urban fabric will be based on maps (x, and y dimensions). Considering archaeological and historical approaches, urban fabric can be studied in considering many aspects such as the functions of the buildings and the districts, the mobility of the people within the city, and more broadly about beliefs, knowledges, traditions and symbols from the Roman period. Considering a geoarchaeological approach, river mouth environments are particularly dynamic contexts. River channels move laterally and coastlines are regularly affected by sedimentation or erosion. In consequence, settlements located in river mouth environments have to adapt to maintain harbour interfaces between the land and the river channels or between the land and the sea. Second, we will be exploring the verticality of the urban fabric. The z height dimension will include stratigraphic data in particular. The concept of archaeosphere will be discussed and apply to our datasets. We will try to show how archaeological and palaeoenvironmental data can be integrated to better define the archaeosphere and its dynamic through time. These aspects will be further developed within the FNRS project “Early Ostia Revisited - EOR”. Finally, over the years and centuries, urban fabrics record the successive adjustments of the settlements to the fluvial and coastal mobility and vertical instability. Case studies will be used to characterise anthropic and natural factors that are both relevant to better understand urban fabrics of Roman river mouth settlements. We will insist on the fact that urban fabric should definitely be discussed by archaeologists, historians, geoarchaeologists but also architects, and urbanists.