Titus Livius (Livy), The History of Rome, Book 2
Rev. Canon Roberts, Ed.

11. Repulsed¹ in his first attempt, Porsena changed his plans from assault to blockade. After placing a detachment to hold the Janiculum he fixed his camp on the plain between that hill and the Tiber, [2??] and sent everywhere for boats, partly to intercept any attempt to get corn into Rome and partly to carry his troops across to different spots for plunder, as opportunity might serve. [3] In a short time he made the whole of the district round Rome so insecure that not only were all the crops removed from the fields but even the cattle were all driven into the City, nor did any one venture to take them outside the gates. [4] The impunity with which the Etruscans committed their depredations was due to strategy on the part of the Romans more than to fear. For the consul Valerius, determined to get an opportunity of attacking them when they were scattered in large numbers over the fields, allowed small forages to pass unnoticed, whilst he was reserving himself for vengeance on a larger scale. [5] So to draw on the pillagers, he gave orders to a considerable body of his men to drive cattle out of the Esquiline gate, which was the furthest from the enemy, in the expectation that they would gain intelligence of it through the slaves who were deserting, owing to the scarcity produced by the blockade. [6] The information was duly conveyed, and in consequence they crossed the river in larger numbers than usual in the hope of securing the whole lot. [7] P. Valerius ordered T. Herminius with a small body of troops to take up a concealed position at a distance of two miles on the Gabian road, whilst Sp. Lartius with some light-armed infantry was to post himself at the Colline gate until the enemy had passed him and then to intercept their retreat to the river. [8] The other consul, T. Lucretius, with a few maniples made a sortie from the Naevian gate; Valerius himself led some picked cohorts from the Caelian hill, and these were the first to attract the enemy's notice. [9] When Herminius became aware that fighting was begun, he rose from ambush and took the enemy who were engaged with Valerius in rear. [10] Answering cheers arose right and left, from the Colline and the Naevian gates, and the pillagers, hemmed in, unequal to the fight, and with every way of escape blocked, were cut to pieces. That put an end to these irregular and scattered excursions on the part of the Etruscans.