On the seventh day of the siege, a great wind having arisen, the enemies threw into the camp fiery darts, and launched from their slings balls of burning clay (_ferventes fusili ex argilla glandes_).[434] The barracks, roofed with straw, in the Gaulish manner, soon took fire, and the wind spread the flames in an instant through the whole camp. Then, raising great shouts, as though they had already gained the victory, they pushed forward their towers and covered galleries, and attempted, by means of ladders, to scale the _vallum_; but such were the courage and steadiness of the Roman soldiers, that, though surrounded with flames, overwhelmed with a shower of darts, and knowing well that the fire was devouring their baggage and their property, not one of them quitted his post, or even dreamt of turning his head, so much did that desperate struggle absorb their minds. This was their most trying day. Meanwhile, many of the enemies were killed and wounded, because, crowding to the foot of the rampart, the last ranks stopped the retreat of the first. The fire having been appeased, the barbarians pushed up a tower against the _vallum_.[435] The centurions of the third cohort, who happened to be there, drew their men back, and, in bravado, invited, by their gesture and voice, the enemies to enter. Nobody ventured. Then they drove them away by a shower of stones, and the tower was burnt. There were in that legion two centurions, T. Pulio and L. Vorenus, who emulated each other in bravery by rushing into the midst of the assailants. Thrown down in turn, and surrounded by enemies, they mutually rescued each other several times, and returned into the camp without wounds. Defensive arms then permitted individual courage to perform actual prodigies. Still the siege continued, and the number of the defenders diminished daily; provisions began to fall short, as well as the necessaries for tending the wounded.[436] The frequent messengers sent by Cicero to Cæsar were intercepted, and some of them cruelly put to death within view of the camp. At last, Vertico, a Nervian chieftain who had embraced the cause of the Romans, prevailed upon one of his slaves to take charge of a letter to Cæsar. His quality of a Gaul enabled him to pass unperceived, and to give intelligence to the general of Cicero’s danger.