The westward and southward pressure of the Germans, then a very powerful and numerous people, was in full force in Cæsar's time, so much so that it seems certain that Cæsar's conquest of Gaul came just in time to stay and delay that tide of Germanic invasion which overran Gaul some centuries later. His first operations in Gaul were against the Helvetii, whose country corresponded to the modern Switzerland. He tells us that the Belgae are at continual war with the Germans along the Rhine, and also that the Helvetii in their own country fight almost daily battles with the Germans. In the first year of Cæsar's Gallic command, the Helvetii came to a decision to migrate from their country westward, and Cæsar's first campaign was conducted with the purpose of forcing them to return to their own country. He ordered them to return thither, he states, lest the Germans should take possession of the territory and thus become neighbours to the old Roman province in southern Gaul.

Cæsar states plainly that the Belgae for the most part are of German origin; that in former times they had crossed the Rhine and dispossessed the Galli (here he used the name Galli as proper to the other inhabitants of Gaul in distinction from the Belgae). He indicates that, after this migration, they had offered a successful resistance to the invasion of the Cimbri and Teutones (between 113 and 102 B.C.).

Modern Frenchmen, though their national name is in origin the name of a Germanic people, show a tendency, easily understood, to minimise the Germanic element in their composition, and M. D'Arbois de Jubainville, dealing with Cæsar's statement that the Belgae were mainly of Germanic origin, seeks to explain that this was true geographically not ethnographically, that they came from German lands but did not come of German ancestry. Against the plain statement of a contemporary observer, such explanations are always to be received with caution. In this instance, there is corroborative evidence which indicates that Cæsar's words are to be taken at their face value. Cæsar also tells us that the Condrusi, Eburones, Cærosi and Paemani "uno nomine Germani vocantur"—are called by the common name of Germans. Again he says that the Segni and Condrusi are "ex gente et numero Germanorum"—of the German nation and so accounted. Strabo, writing within a century of Cæsar, says that "the Nervii are a Germanic people." According to Cæsar, the Nervii had no commerce, avoided wine and other luxuries, and were fierce men of great valour. They led the rest of the Belgae in opposing him. Tacitus is a hardly less valid authority, for his father-in-law Agricola had been engaged in long campaigns against the Germans in the Rhine country. "The Treveri and the Nervii," he says, "are especially forward in asserting their German origin, as though by this boast of race to be distinguished from the pacific character of the Gauls." It was surely not a geographical origin that was claimed in such a way. 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.

It seems to me, then, to be certain that the Belgae not only came into Gaul from Germany, but were themselves a mixed population of Celts and Germans speaking a Celtic dialect. Holder assigns their migration into Gaul to the third century B.C. It is, however, undesirable to attempt to fix anything but a somewhat extended period for migratory movements of the kind. The instance of the Helvetii proves that down to Cæsar's time the Celts in contact with the Germans were still in a very mobile condition.

Before using the facts hitherto stated and the conclusions derived from them to throw whatever light they can on the Celtic colonisation of Ireland, it may be well to state in a general way what can be said as to the stage of civilisation reached by the continental Celts before their subjugation by the Romans.

Some modern writers, but not very recently, have written about a Celtic Empire in ancient Europe. The nearest approach to authority for the existence of such an empire is a statement by Livy, who says: "While the elder Tarquin reigned in Rome, the supremacy among the Celts belonged to the Bituriges. They gave a king to the Celtic land. Ambigatus was his name, a very mighty man in valour and in his private and public resources, under whose rule Gaul was so abounding in men and in the fruits of the earth that it seemed impossible to govern so great a population."

The most that can be made of this passage, supposing that Livy had it on better authority than some other parts of his history, is that at one time the Bituriges held what the Greeks called hegemony, a political primacy among the Gauls, and this, too, only in the time of a single king. It may reflect a genuine Celtic tradition, going back to the time when the Celts were still a compact nation inhabiting a relatively small territory.