Our knowledge of the civitates of the Treveri and Mediomatrici in the late Iron Age stems primarily from Caesar’s descriptions in the account of his deeds, the Commentarii Belli Gallici. In the Gallo-Roman period, both names survived as denominations of administrative units within the province of Gallia Belgica. These terms certainly refer to historical realities, although on closer inspection their meaning is difficult to define precisely. Issues arise from the names themselves, for neither do we know how Caesar acquired his knowledge of these names nor to what they corresponded. Furthermore the translation of the noun civitas (in Latin, usually a term for the community of citizens from a town, township or state) causes difficulties in connection with the population groups of late Iron Age Gaul. Often, this descriptor is translated as ‘tribe’, ‘group of tribes’, ‘people’ or ‘nation/ethnic group’. However, we know today that archaeological cultures cannot be readily equated with such identity-groups. This article initially advances general thoughts regarding the denomination of ‘tribes’ and ‘ethnic groups’ in the context of evolutionary biology and ethnographic research. Then, based on the latest research, the question to be addressed is whether and how the Treveri and Mediomatrici are manifested as archaeological cultures and how these entities can be distinguished from one another in a prehistoric context. Finally, a hypothesis on the identity of the Treveri is formulated.