The “hedgehog”[278] will be found an effective device in defending a castle. It is made of large, heavy beams armed along the ridge with a brush of pointed oak nails; it is hung outside the parapet to be dropped on anyone who comes too near the wall. Turnpikes made of large heavy logs armed with sharp teeth of hard oak may be raised on end near the battlements and kept ready to be dropped upon those who approach the castle. Another good device is the “briar,”[279] which is made of good iron and has curved thorns as hard as steel with a barb on every thorn; and the chain, from which it hangs, as high up as a man can reach must be made of spiked links, so that it can be neither held nor hewn; higher up any kind of rope that seems suitable may be used, only, it must be firm and strong. This briar is thrown down among the enemy in the hope of catching one or more of them and then it is pulled up again. A “running wheel”[280] is also a good weapon for those who defend castles: it is made of two millstones with an axle of tough oak joining them. Planks sloping downward are laid out through the openings in the wall; the wheel is rolled out upon these and then down upon the enemy. Footnote 278: The hedgehog (_ericius_) in common use was a form of the _cheval de frise_ and was laid on the earth to impede a hostile advance. I know of no other mention of the device (_igelkǫttr_) described above. Footnote 279: Captain Blom is disposed to look on the _brynklungr_ as an imaginary device (_Aarböger for nordisk Oldkyndighed_, 1867, 106) but Falk finds that some such instrument was in use in Italy as early as the tenth century (_Altnordische Waffenkunde_, 199-200). Footnote 280: Devices somewhat similar to the “running wheel” seem to have been used in medieval warfare, but of this particular form no other mention has been found. See Falk, _Altnordische Waffenkunde_, 200.