Titus Livius (Livy), The History of Rome, Book 10
Rev. Canon Roberts, Ed.

4. The news of this defeat created a quite unnecessary alarm in Rome. Measures were adopted as though an army had been annihilated; [2] all legal business was suspended, guards were stationed at the gates, watches were set in the different wards of the City, armour and weapons were stored in readiness on the walls, and every man within the military age was embodied.

[3] When the Dictator returned to the camp he found that, owing to the careful arrangements which the Master of the Horse had made, everything was quieter than he had expected. [4] The camp had been moved back into a safer position; the cohorts who had lost their standards were punished by being stationed outside the rampart without any tents; [5] the whole army was eager for battle that they might all the sooner wipe out the stain of their defeat. [6] Under these circumstances the Dictator at once advanced his camp into the neighbourhood of Rusella. The enemy followed him, and although they felt the utmost confidence in a trial of strength in the open field, they decided to practise stratagem on their enemy, as they had found it so successful before. [7] At no great distance from the Roman camp were some half-demolished houses belonging to a village which had been burnt when the land was harried. [8] Some soldiers were concealed in these and cattle were driven past the place in full view of the Roman outposts, who were under the command of a staff-officer, Cnaeus Fulvius. As not a single man left his post to take the bait, one of the drovers, coming up close to the Roman lines, called out to the others who were driving the cattle somewhat slowly away from the ruined cottages to ask them why they were so slow, as they could drive them safely through the middle of the Roman camp. [9] Some Caerites who were with Fulvius interpreted the words, and all the maniples were extremely indignant at the insult, but they did not dare to move without orders. [10] He then instructed those who were familiar with the language to notice whether the speech of the herdsmen was more akin to that of rustics or to that of towndwellers. On being told that the accent and personal appearance were too refined for cattle-drovers, he said, ‘Go and tell them to unmask the ambush they have tried in vain to conceal; the Romans know all, and can now no more be trapped by cunning than they can be vanquished by arms.’ [11] When these words were carried to those who were lying concealed, they suddenly rose from their lurking-place and advanced in order of battle on to the open plain, which afforded a view in all directions. [12] The advancing line appeared to Fulvius to be too large a body for his men to withstand, and he sent a hasty message to the Dictator to ask for help; in the meantime he met the attack single-handed.