ōgi-no-nawa 扇の縄

Also written 扇子の縄. A castle plan shaped like a folding fan wherein the fortifications are distributed on either side of the castle water supply. In the case of mountain castles where the water supply was typically located below the mountain top in a valley lake, a fortification would be built there to guard the water source. The main compound located at the mountaintop would be sited where the pivot of the folding fan would be. A wall or embankment was built along the curve of the fan to protect the water source.