Katō

The country later called Katō lay along the northern side of the Tokachi river system in eastern Hokkaido. Before the nineteenth-century districts were created, it formed part of the world of Ainu settlements and routes along the rivers. Earthworks known as chashi occupied prominent ground overlooking the water. The Tokachi region contains many such sites, including examples beside the Tokachi and Otofuke rivers.

Chashi were built during approximately the sixteenth to eighteenth centuries. Their defining features include ditches across or around a hilltop and, probably, wooden fencing. Their functions were varied and remain debated: traditions associate them with defence, watching, ceremony and negotiations to settle disputes. They should not all be treated as identical military castles. These river-facing sites show how Ainu communities organised important places within their own landscape. In 1800, Minagawa Shūdayū surveyed the Tokachi river system under official orders. This growing external interest preceded the later administrative divisions and mass agricultural settlement that transformed the country.