A “shot wagon”[281] is also a good device. This is made like any other wagon with two or four wheels as one likes and is intended to carry a load of stones, hot or cold as one may prefer. It must also be provided with two firm and strong chains, one on each side, which can be depended on to check the wagon even where it has a long track to run upon. It is meant to run on planks set with a downward slope, but one must be careful to keep the wheels from skidding off the planks. When the chains check the speed, the wagon shoots its load out upon the men below. The more uneven the stones are, some large and some small, the more effective the load will be. Canny men, who are set to defend a wall and wish to throw rocks down upon the attacking line or upon the penthouse, make these rocks of clay with pebbles, slingstones, and other hard stones placed inside. The clay is burned hard enough on the outside to endure the flight while the load is being thrown; but as soon as the rocks fall they break into fragments and consequently cannot be hurled back again. To break down stone walls, however, large, hard rocks are required. Similarly, when one hurls missiles from a stone fortress against an opposing wooden tower or upon the axletrees which support siege engines, towers, scaling ladders, cats, or any other engine on wheels, the larger and harder the rocks that are used, the more effective they will be. Footnote 281: _Ibid._ The “shot wagon” is not mentioned elsewhere. Boiling water, molten glass, and molten lead are also useful in defending walls.[282] But if a cat or any other covered engine which cannot be damaged by hot water is being pushed toward a castle, it is a good plan, if the engine is lower than the walls, to provide beams carefully shod with iron underneath and in addition armed with large, sharp, red-hot plowshares. These are to be thrown down upon the wooden engine in which the plowshares are likely to stick fast, while the beams may be hoisted up again. This attack should be followed up with pitch, sulphur, or boiling tar.[283] Footnote 282: See the Sorö edition, 424-425, where the editor cites a number of references to the use of fire in defensive warfare; these are nearly all drawn from the sagas. Footnote 283: Evidently the purpose would be to crush the engine with the beam, to set it on fire with the hot plowshares, and to put the assailants to flight with the pitch, sulphur, or tar; these would also feed the flames.