Abstract : An archaeological, historical and technological research on the mud brick buildings in Dura-Europos has been conducted from 1994 to 2000. It showed the importance of the study of the materials in leading such a research, because these are often the only elements which can be used to associate or to differentiate several walls. So, the Hellenistic part of the mud brick fortifications, which is examined here, has been characterized, defined and its limits have been set of. In this way, several walls, often separated in space, have been linked up and the chronology of the building of the rampart has been determined. Therefore. this study contributed to give a better knowledge of the town's history and of its city planning development.