C. Julius Caesar, Gallic War

To the extraordinary valor of our soldiers, devices of every sort were opposed by the Gauls; since they are a nation of consummate ingenuity, and most skillful in imitating and making those things which are imparted by any one; for they turned aside the hooks with nooses, and when they had caught hold of them firmly, drew them on by means of engines, and undermined the mound the more skillfully on this account, because there are in their territories extensive iron mines, and consequently every description of mining operations is known and practiced by them. They had furnished, more over, the whole wall on every side with turrets, and had covered them with skins. Besides, in their frequent sallies by day and night, they attempted either to set fire to the mound, or attack our soldiers when engaged in the works; and, moreover, by splicing the upright timbers of their own towers, they equaled the height of ours, as fast as the mound had daily raised them, and countermined our mines, and impeded the working of them by stakes bent and sharpened at the ends, and boiling pitch and stones of very great weight, and prevented them from approaching the walls.