Day after day was passing in this manner, when Cæsar was informed of the arrival of C. Trebonius and his troops, which raised the number of his legions to seven. The chiefs of the Bellovaci then feared an investment like that of Alesia, and resolved to quit their position. They sent away by night the old men, the infirm, the unarmed men, and the part of the baggage which they had kept with them. Scarcely was this confused multitude in motion, embarrassed with its own mass and its numerous chariots, when daylight surprised it, and the troops had to be drawn up in line before the camp, to give the column time to move away. Cæsar saw no advantage either in giving battle to those who were in position, or, on account of the steepness of the hill, in pursuing those who were making their retreat; he resolved, nevertheless, to make two legions advance in order to disturb the enemy in his retreat. Having observed that the mountain on which the Gauls were established was connected with another height (Mont Collet), from which it was only separated by a narrow valley, he ordered bridges to be thrown on the marsh; the legions crossed over them, and soon attained the summit of the height, which was defended on both sides by abrupt declivities. There he collected his troops, and advanced in order of battle up to the extremity of the plateau, whence the engines, placed in battery, could reach the masses of the enemy with their missiles. The barbarians, rendered confident by the advantage of their position, were ready to accept battle, if the Romans dared to attack the mountain; besides, they were afraid to withdraw their troops successively, as, if divided, they might have been thrown into disorder. This attitude led Cæsar to resolve on leaving twenty cohorts under arms, and on tracing a camp on this spot, and retrenching it. When the works were completed, the legions were placed before the retrenchments, and the cavalry distributed with their horses bridled at the outposts. The Bellovaci had recourse to a stratagem in order to effect their retreat. They passed from hand to hand the fascines and the straw on which, according to the Gaulish custom, they were in the habit of sitting, preserving at the same time their order of battle, placed them in front of the camp, and, towards the close of the day, on a preconcerted signal, set fire to them. Immediately a vast flame concealed from the Romans the Gaulish troops, who fled in haste.