The Romans had been able to see these preparations from the summit of the tower; moreover, they stationed a strong guard on the flanks of the plateau every evening. The legate at nightfall had these points protected by stakes, and had a quantity of _stimuli_ (Fig. 11) driven into the ground outside. About the third hour of the night the besieged issued noiselessly from the two gates and came within half a bowshot of the Roman posts. At a signal given from the interior, the two bodies rushed at once on the besiegers' flanks. But even before they could reach the palisades, many of them, wounded by the _stimuli_, fell uttering cries of pain. Those who reached the besiegers' posts, thinned by the darts showered upon them, and hesitating on seeing so many of their party fall, were more inclined to fly than to continue the attack when they saw themselves in their turn taken in flank and rear by the besiegers. The defenders on the ramparts, whom the darkness of the night prevented from seeing clearly what was taking place, and not knowing whether the confusion arose from the flight of the Romans or of their own men, dared not discharge stones and arrows.
Meanwhile the lighted barrels were being rolled in front of the galleries, which had already begun to take fire. By the glare of the flames they could see the Roman soldiers mount on the terrace carrying baskets full of wet earth, which they threw on the barrels; and the defenders killed or wounded many of them. At this moment some of the fugitives who had taken part in the two sorties, re-entered the camp calling out that they were pursued by the Romans.
Catognatus had barely time to send troops to defend the two egresses and to protect the retreat of his men. He himself took up a position in the centre of the Oppidum with a chosen band, that he might be able to assist the quarter that should be most closely pressed. Aided by this diversion the Romans, less harassed by darts from the rampart, were able to extinguish the fire. They took advantage of the last hours of the night to advance the tower along the galleries by means of rollers, as far as the edge of the _agger_, and in the morning the warriors of the Val d'Avon were not a little surprised to see this ponderous wooden structure commanding the whole rampart and the towers of the defences.