daiin-no-koguchi 大陰の虎口

Also written 大陰虎口. A simple, early form of castle entrance *koguchi 虎口, constructed by cutting a single passageway through an earthen embankment *doi 土居. Usually about 6 m (3 *ken 間) wide. The lack of protective features made it very difficult for the castle forces to go out and drive off an enemy, and enemy forces had a direct entry route to the castle. Therefore the daiin-no-koguchi did not prove effective in battle, and more complex castle entrances were subsequently developed. The first devices to be added were cross-over embankments *kuichigai 喰違, overhanging doors *shitomi 蔀, and barriers or enclosing walls shōheki 障壁.