Titus Livius (Livy), The History of Rome, Book 24
Frank Gardener Moore, Professor Emeritus in Columbia University, Ed.

46. Fabius setting out from Suessula first pressed the siege of Arpi. There he pitched his camp at a distance of about five hundred paces, and after observing the situation of the city and the walls at close range, he decided to attack just at that part of the city which was best defended by walls, because he saw that that was the most carelessly guarded. [2] He assembled everything useful for siege operations, selected from the entire army the pick of the centurions, and placed tribunes who were brave men in command of them. And he assigned them six hundred soldiers —all that seemed necessary —and ordered them to carry ladders to that place, when the trumpet should sound for the fourth watch. [3] There was a low, narrow gate there, as the street, leading through a deserted part of the city, was not much frequented. He ordered them first to climb over the wall by means of their ladders, and then to open that gate from the inside, or else break down the bars, and then, holding a part of the city, to give the signal on a trumpet for the rest of the troops to move up. He would have everything ready and in order. [4] These commands were carried out with spirit, and a circumstance which seemed likely to hamper action proved of the greatest help to secrecy. Heavy rain beginning at midnight forced the guards and sentries to slip away from their posts and run to cover. [5] And the sound, at first of a heavier shower, prevented the noise they made in forcing the gate from being heard clearly, and then, gentler and more monotonous as they listened, it lulled a great many [p. 325]of the men to sleep. [6] Once in possession of the gate,¹ they ordered the trumpeters, posted at equal intervals along the road, to sound, in order to summon the consul. [7] This done according to agreement, the consul orders the standards to be carried out of the camp, and a little before daylight enters the city through the gate they had forced.