This is regarded as facilities to drain the water away so that the rainwater running down from the slope of the mountain might not burst the earth mounds, which is thought to be a unique device that cannot be found in the construction of yamajiro in the Chinese continent.
山の斜面からの雨水で土塁が決壊しないように排水した設備と見られ、大陸の山城築城にはない独自の工夫とみられる。