Titus Livius (Livy), The History of Rome, Book 32
Evan T. Sage, Ph.D. Professor of Latin and Head of the Department of Classics in the University of Pittsburgh, Ed.

11. When matters were in this state, a shepherd, sent by Charopus, a leading man of Epirus, was brought before the consul. [2] He said that he had been accustomed to pasture his flocks in the valley which the king's camp then occupied, and knew all the tracks and paths of those hills. [3] If the consul wished to send some men with him, he would guide them by a road, quite level and not very difficult, to a place commanding the enemy's position. [4] The consul, on hearing this, sent to Charopus to inquire whether he thought the shepherd should be trusted in so important a matter. Charopus ordered the message back to be that he should trust him, but only so far as to keep the control of the situation in his own hands rather than in the shepherd's. Wishing, [5] rather than venturing, to trust him, and with feelings of mingled joy and apprehension, he was persuaded by the assurances of Charopus and determined to use the chance presented to him, [p. 185]and, to prevent the king [6] from suspecting, he did not¹ cease for two successive days to attack the enemy, posting detachments on all sides and sending fresh troops to relieve the weary. Then he put a tribune in command of four thousand picked infantry and three hundred cavalry. [7] He ordered him to take the cavalry as far as the ground permitted; when the road became impassable for cavalry, he should leave them on some level spot and go with the infantry wherever the guide conducted them; [8] when he reached, as the guide promised, the place above the enemy, the tribune should send up a smoke-signal but raise no shout until, after the answering signal had been received from him, he could judge that the battle had begun. He instructed the tribune to march by night —and the moon happened to be full —and by day to take time for food and rest. [9] The guide, loaded with magnificent promises, if he should keep faith, but nevertheless in chains, he turned over to the tribune. [10] Having thus sent out his troops, the Roman pressed the attack the more vigorously from all sides, selected vantage-grounds.²