A rope, traditionally of twisted straw and adorned with hanging strips of straw, zig-zag paper or cloth streamers (yu, shide, representing offerings). Its function, like the torii, is to delimit a tabooed, sacred or purified space. A shimenawa is often hung between the posts of a torii under the cross bar(s); indeed a shimenawa between two posts may have been the prototype of the torii. It is used to enclose himorogi, temporary ritual areas (e.g. for jichinsai), to mark sacred trees or rocks or to decorate buildings including shrines and houses at special or festival times. Shimenawa vary in size and shape from a simple narrow rope to stylized, usually tapered and exaggeratedly thick hawsers up to six feet in diameter. The mythical origin of the shimenawa is said to be the bottom-tied-rope (shiri-kume-nawa) which according to the Kojiki and Nihongi was used by the kami Futo-tama to prevent Amaterasu from returning to the cave in which she had concealed herself, once she had been lured out. According to the Kogoshui the rope encircled the new palace built for Amaterasu.
See also Shimekazari.
A Popular Dictionary of Shinto. Brian Bocking.