XXII.--To the extraordinary valour of our soldiers, devices of every sort were opposed by the Gauls; since they are a nation of consummate ingenuity, and most skilful 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 skilfully on this account, because there are in their territories extensive iron mines, and consequently every description of mining operations is known and practised by them. They had furnished, moreover, 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 equalled 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. XXIII.--But this is usually the form of all the Gallic walls. Straight beams, connected lengthwise and two feet distant from each other at equal intervals, are placed together on the ground; these are mortised on the inside, and covered with plenty of earth. But the intervals which we have mentioned, are closed up in front by large stones. These being thus laid and cemented together, another row is added above, in such a manner that the same interval may be observed, and that the beams may not touch one another, but equal spaces intervening, each row of beams is kept firmly in its place by a row of stones. In this manner the whole wall is consolidated, until the regular height of the wall be completed. This work, with respect to appearance and variety, is not unsightly, owing to the alternate rows of beams and stones, which preserve their order in right lines; and, besides, it possesses great advantages as regards utility and the defence of cities; for the stone protects it from fire, and the wood from the battering ram, since it [the wood] being mortised in the inside with rows of beams, generally forty feet each in length, can neither be broken through nor torn asunder.