One of the objects which Caesar had proposed to himself - the subjugation of Gaul - had been in substance, with exceptions scarcely worth mentioning, attained so far as it could be attained at all by the sword. But the other half of the work undertaken by Caesar was still far from being satisfactorily accomplished, and the Germans had by no means as yet been everywhere compelled to recognize the Rhine as their limit. Even now, in the winter of 698-699, a fresh crossing of the boundary had taken place on the lower course of the river, whither the Romans had not yet penetrated. The German tribes of the Usipetes and Tencteri whose attempts to cross the Rhine in the territory of the Menapii have been already mentioned[41], had at length, eluding the vigilance of their opponents by a feigned retreat, crossed in the vessels belonging to the Menapii - an enormous host, which is said, including women and children, to have amounted to 430,000 persons. They still lay, apparently, in the region of Nimeguen and Cleves; but it was said that, following the invitations of the Celtic patriot party, they intended to advance into the interior of Gaul; and the rumour was confirmed by the fact that bands of their horsemen already roamed as far as the borders of the Treveri.

But when Caesar with his legions arrived opposite to them, the sorely-harassed emigrants seemed not desirous of fresh conflicts, but very ready to accept land from the Romans and to till it in peace under their supremacy. While negotiations as to this were going on, a suspicion arose in the mind of the Roman general that the Germans only sought to gain time till the bands of horsemen sent out by them had returned. Whether this suspicion was well founded or not, we cannot tell; but confirmed in it by an attack, which in spite of the de facto suspension of arms a troop of the enemy made on his vanguard, and exasperated by the severe loss thereby sustained, Caesar believed himself entitled to disregard every consideration of international law. When on the second morning the princes and elders of the Germans appeared in the Roman camp to apologize for the attack made without their knowledge, they were arrested, and the multitude anticipating no assault and deprived of their leaders were suddenly fallen upon by the Roman army. It was rather a manhunt than a battle; those that did not fall under the swords of the Romans were drowned in the Rhine; almost none but the divisions detached at the time of the attack escaped the massacre and succeeded in recrossing the Rhine, where the Sugambri gave them an asylu in their territory, apparently on the Lippe. The behaviour of Caesar towards these German immigrants met with severe and just censure in the senate; but, however little it can be excused, the German encroachments were emphatically checked by the terror which it occasioned.

Caesar however found it advisable to take yet a further step and to lead the legions over the Rhine. He was not without connections beyond the river. the Germans at the stage of culture which they had then reached, lacked as yet any national coherence; in political distraction they - though from other causes - fell nothing short of the Celts. The Ubii (on the Sieg and Lahn), the most civilized among the German tribes, had recently been made subject and tributary by a powerful Suebian canton of the interior, and had as early as 697 through their envoys entreated Caesar to free them like the Gauls from the Suebian rule. It was not Caesar's design seriously to respond to this suggestion, which would have involved him in endless enterprises; but it seemed advisable, with the view of preventing the appearance of the Germanic arms on the south of the Rhine, at least to show the Roman arms beyond it. The protection which the fugitive Usipetes and Tencteri had found among the Sugambri afforded a suitable occasion. In the region, apparently between Coblentz and Andernach, Caesar erected a bridge of piles over the Rhine and led his legions across from the Treverian to the Ubian territory.

Some smaller cantons gave in their submission; but the Sugambri, against whom the expedition was primarily directed, withdrew, on the approach of the Roman army, with those under their protection into the interior. In like manner the powerful Suebian canton which oppressed the Ubii - presumably the same which subsequently appears under the name of the Chatti - caused the districts immediately adjoining the Ubian territory to be evacuated and the non-combatant portion of the people to be placed in safety, while all the men capable of arms were directed to assemble at the centre of the canton. The Roman general had neither occasion nor desire to accept this challenge; his object - partly to reconnoitre, partly to produce an impressive effect if possible upon the Germans, or at least on the Celts and his countrymen at home, by an expedition over the Rhine - was substantially attained; after remaining eighteen days on the right bank of the Rhine he again arrived in Gaul and broke down the Rhine bridge behind him (699).

There remained the insular Celts. From the close connection between them and the Celts of the continent, especially the maritime cantons, it may readily be conceived that they had at least sympathized with the national resistance, and that if they did not grant armed assistance to the patriots, they gave at any rate an honourable asylum in their sea-protected isle to every one who was no longer safe in his native land. This certainly involved a danger, if not for the present, at any rate for the future; it seemed judicious - if not to undertake the conquest of the island itself - at any rate to conduct there also defensive operations by offensive means, and to show the islanders by a landing on the coast that the arm of the Romans reached even across the Channel. The first Roman officer who entered Brittany, Publius Crassus had already (697) crossed thence to the "tin-island" at the south-west point of England (Stilly islands); in the summer of 699 Caesar himself with only two legions crossed the Channel at its narrowest part[42]. He found the coast covered with masses of the enemy's troops and sailed onward with his vessels; but the British war-chariots moved on quite as fast by land as the Roman galleys by sea, and it was only with the utmost difficulty that the Roman soldiers succeeded in gaining the shore in the face of the enemy, partly by wading, partly in boats, under the protection of the ships of war, which swept the beach with missiles thrown from machines and by the hand. In the first alarm the nearest villages submitted; but the islanders soon perceived how weak the enemy was, and how he did not venture to move far from the shore. The natives disappeared into the interior and returned only to threaten the camp; and the fleet, which had been left in the open roads, suffered very considerable damage from the first tempest that burst upon it. The Romans had to reckon themselves fortunate in repelling the attacks of the barbarians till they had bestowed the necessary repairs on the ships, and in regaining with these the Gallic coast before the bad season of the year came on.

Caesar himself was so dissatisfied with the results of this expedition undertaken inconsiderately and with inadequate means, that he immediately (in the winter of 699-700) ordered a transport fleet of 800 sail to be fitted out, and in the spring of 700 sailed a second time for the Kentish coast, on this occasion with five legions and 2000 cavalry. The forces of the Britons, assembled this time also on the shore, retired before the mighty armada without risking a battle; Caesar immediately set out on his march into the interior, and after some successful conflicts crossed the river Stour; but he was obliged to halt very much against his will, because the fleet in the open roads had been again half destroyed by the storms of the Channel. Before they got the ships drawn up upon the beach and the extensive arrangements made for their repair, precious time was lost, which the Celts wisely turned to account.