On Ditches at the Ancient Capital Cities in Japan

Ditches are constructed at both sides of a street at the ancient capital cities in Japan. As the streets are laid out in a grid pattern, the ancient cities have the network of drainage by ditches. In this paper, the network of drainage in Nagaokakyo and Heiankyo is discussed. The dimensions and the connection of ditches are made clear using historical literature and the archaorogical excavation data. Considering the topography, the flow of drainage are examined. The character of ditches and the plan of storm water drainage between Nagaotakyo and Heiankyo is different from each other.