These formidable retrenchments had a double aim: to increase the confidence of the barbarians, by making them believe that they were feared; and, next, to allow the number of the garrison to be reduced with safety, when they had to go far for provisions. For some days there were no serious engagements, but slight skirmishes in the marshy plain which extended between the two camps. The capture, however, of a few foragers did not fail to swell the presumption of the barbarians, which was still more increased by the arrival of Commius, although he had brought only 500 German cavalry. The enemies remained for several days shut up in their impregnable position. Cæsar judged that an assault would cost too many lives; an investment alone seemed to him opportune, but it would require a greater number of troops. He wrote thereupon to Trebonius to send him as soon as possible the 13th legion, which, under the command of T. Sextius, was in winter quarters among the Bituriges; to join it with the 6th and the 14th, which the first of these lieutenants commanded at Genabum, and to come himself with these three legions by forced marches. During this time he employed the numerous cavalry of the Remi, the Lingones, and the other allies, to protect the foragers and to prevent surprises. But this daily service, as is often the case, ended by being negligently performed; and one day the Remi, pursuing the Bellovaci with too much ardour, fell into an ambuscade. In withdrawing, they were surrounded by foot-soldiers, in the midst of whom Vertiscus, their chief, met with his death. True to his Gaulish manner, he would not allow his age to dispense him from commanding and mounting on horseback, although he was hardly able to keep his seat. His death and this feeble advantage raised the self-confidence of the barbarians still more, but it rendered the Romans more circumspect. Nevertheless, in one of the skirmishes which were continually taking place within sight of the two camps, about the fordable places of the marsh, the German infantry, which Cæsar had sent for from beyond the Rhine, in order to mix them with the cavalry, joined in a body, boldly crossed the marsh, and, meeting with little resistance, continued the pursuit with such impetuosity that fear seized not only the enemies who fought, but even those who were in reserve. Instead of availing themselves of the advantages of the ground, all fled cowardly; they did not stop till they were within their camp, and some even were not ashamed to fly beyond it. This defeat caused a general discouragement, for the Gauls were as easily damped by the least reverse as they became arrogant on the smallest success.