 Caesar seems to be one of the first authors to distinguish the two groups, and he had a political motive for doing so (it was an argument in favour of the Rhine border).Yet, one cannot always trust Caesar and Tacitus when they ascribe individuals and tribes to one or the other category, although Caesar made clear distinctions between the two cultures.Most ancient sources categorize the Cimbri as a Germanic tribe, but some ancient authors include the Cimbri among the Celts.