The Treveri dwelt on the west side of the Rhine. They were a Celtic-speaking people, and unlike most of the inhabitants of Gaul they seem to have retained their Celtic language throughout the period of Roman domination, for St. Jerome, writing in the late part of the fourth century, says that "the Galatians (of Asia Minor), apart from the Greek language, which all the East speaks, have a language of their own almost the same as the Treveri." In one respect the Treveri, Cæsar tells us, resembled the Germans of his time--they excelled in cavalry; and his continuator, Hirtius, writes that "in fierceness and in manner of life they differed little from the Germans." The Advatuci, he writes, "were descendants of the Cimbri and Teutoni." All these peoples dwelt in Belgic Gaul and came under the common appellation of Belgae. In addition to Cæsar's statement that the Belgae as he learned, not supposed, were, for the most part of German origin, we have detailed evidence that, of about eighteen States composing Belgic Gaul, no fewer than eight, in Cæsar's time and long after it, were still accounted to be German. On the other hand, then and afterwards, a number of peoples reckoned to be Celtic continued to inhabit countries to the east of the Rhine. The Tencteri and the Usipetae, on the German side of the Rhine, were Celts, according to Dio Cassius. Tacitus, speaking of the Helvetii and the Boii, says that "both are Gallic nations," yet in another passage he speaks of "the Boii, a nation of the Germans." Still further east dwelt the Cotini and the Osi, of whom he writes: "The Cotini by their use of the Gallic language and the Osi by their use of the Pannonic language are proved not to be Germans": from which it appears that language was the criterion by which the Romans were accustomed to distinguish Germans from Celts. Again Tacitus writes: "The Triboci, Vangiones and Nemetes are certainly Germans," but modern German authorities recognise that the Triboci and Nemetes are Celtic in these very names. Of the Aestyi, dwelling apparently on the northern seaboard of Germany, Tacitus says that their language resembles that of Britain. Further evidence of Celtic occupation of regions considered German in Cæsar's time and ever since then is afforded by a number of ancient place-names. For example, there were two towns or stations named Carrodunon, _i.e._ "wagon-fortress," one on the river Oder, the other in the upper valley of the Vistula. Other Celtic place-names, like Lugidunum, Eburodunum, Meliodunum, are found in central Germany. Tacitus confirms the evidence of Cæsar to the effect that the Belgae were a Germano-Celtic people who came westward over the Rhine and conquered part of the country already occupied by the Celts. "Those," he says, "who first crossed the Rhine and expelled the Gauls were then named Germans but now Tungri." The Tungri inhabited a part of Belgic Gaul between the Nervii and the Treveri.