With this study I would like to clarify the range and social stratification of political territories in ancient Japan (Kofun Period). Since I think that the extent of irrigation reflects the range of the territory of a powerful clan, and that the dispersion of the ancient tombs (Kofun) shows the movement of such a clan, I decided to analyze the relation between the position of ancient tombs and irrigation area. I focused on the situation in the Yodo River Basin. In addition, I investigated the regional structure and the formative process of the Kinai-Region, which consisted of various socially stratified territories. Through my research it became clear to me that there were three different kinds of territories in the ancient Yodo Valley. The Basin of the Yodo River was divided into more than thirty fundamental units lead by local heads. Among those heads there were four powerful leaders who ruled over several uni-fied fundamental units. Their territories ranked above that of the local heads. But it seems that the Yodo River Basin, as a whole, was a unified territory ranking highest.
In conclusion, I think that one can distinguish three different ranks of territory in the Yodo River Basin. Furthermore, I conclude that this Yodo Valley, together with the Yamato Valley constituted the Kinai-Region. It is said that the Kinai-Region was the territory under the direct rule of the Yamato sovereign. Indeed, originally the area under the direct supervision of Yamato rulers was only the Yamato Valley. But in 5th Century the Yodo Valley was incorporated and at this time the spatial structure of the Kinai-Region took shape. So, although one usually assumes that the Kinai-Region is the central region which surrounded the capital city of the Japanese ancient nation in 7th century, I think that the prototype of its spatial structure had already been completed in the 6th Century.
