On the subject of the movable tower see Oman, _Art of War_, 134-135, 549. Those who have to defend a castle may also make use of these weapons which I have now enumerated and many more: trebuckets both large and small, hand slings and staff slings. They will find crossbows and other bows, too, very effective, as well as every other type of shooting weapons, such as spears and javelins both light and heavy. But to resist the trebuckets, the cat, and the engine called the ram, it is well to strengthen the entire stone wall on the inside with large oaken timbers; though if earth and clay are plentiful, these materials had better be used. Those who have to defend castles are also in the habit of making curtains of large oak boughs, three or even five deep, to cover the entire wall;[276] and the curtain should be thoroughly plastered with good sticky clay. To defeat the attacks of the ram, men have sometimes filled large bags with hay or straw and lowered them with light iron chains in front of the ram where it sought to pierce the wall. It sometimes happens that the shots fall so rapidly upon a fortress that the defenders are unable to remain at the battlements; it is then advisable to hang out brattices made of light planks and built high enough to reach two ells above the openings in the parapet and three ells below them. They should be wide enough to enable the men to fight with any sort of weapons between the parapet and the brattice wall, and they should be hung from slender beams in such a way that they may be readily drawn in and hung out again later, as one may wish.[277] Footnote 276: These curtains were evidently placed on the outer side of the wall. Footnote 277: This translation of _hengivigskarð_ is based on Blom’s interpretation (_Aarböger for nordisk Oldkyndighed_, 1867, 105-106, note). The brattices were projecting galleries built along the top of the wall and were in use before it became customary to build stone parapets. Cf. Oman, _Art of War_, 534.