Cæsar’s method of besieging Alesia was dictated by the probability that, with an enemy on both sides, he would have to stand a siege himself. After a doubtful battle, the Gallic army of relief made a night attack on the lines, in which they found to their cost the effectiveness of Cæsar’s death-traps. They brought with them hurdles, with which to help themselves across the ditches, and scaling ladders and grappling hooks, with the help of which they might climb or pull down the rampart. Their weapons were slings, arrows, and stones, to which the Romans replied with extemporised slings and spears. They suffered two repulses, and then turned their attention to the weakest of Cæsar’s camps, while Vercingetorix left Alesia to attack the rampart. His force brought hurdles with long balks of timber to form a footway across them, mantlets, or coverings under which an attacking party, sheltered from Roman missiles, could undermine or make a breach in Cæsar’s earthwork by the use of a bore, and hooks with which to cut down the rampart on the top of the earthen bank. The attack was long and determined. The Gallic pioneers filled up Cæsar’s fosses, so far as they could, with earth, and themselves raised a mound from which his devices of defence were easily seen. Where his lines were on level ground, they were too formidable to attack: on the steep slopes of the hills, on the tops of which his camps were pitched, there was more chance for an enemy. Here the fiercest fighting took place: the towers of the _vallum_ were assailed with javelins, the ditch was filled, and an attempt was made to tear down the palisade and breastwork. Labienus, unable to hold the lines, sent a message to Cæsar, whose intervention with his cavalry turned the day and brought about the total defeat of the Gallic army and the surrender of Vercingetorix.