Chashi

Chashi (チャシ also 砦^?) is the Japanese term for the hilltop fortifications of the Ainu. The word is of Ainu origin, from casi, which means palisade or palisaded compound; a rival theory relates the term to cas. Over 520 chashi have been identified in Hokkaidō, mostly in the eastern regions of the island; others are known from southern Sakhalin and the Kurils; similar phenomena such as the ostrogu of Kamchatka and the gorodische of northeast Asia may have developed independently. A few, including the Tōya casi of present-day Kushiro, date to the Muromachi period; the remainder date largely to the early seventeenth century. As such their construction may be related to increased competition for resources as a result of "intensification of trade" with the Japanese.

The early Dutch explorer Maarten Gerritsz Vries described the chashi he encountered in eastern Hokkaidō in 1643:

These forts were made as follows: on the mountain on which they were placed was a small road steep to climb, and round on the four sides palisades were placed of the height … of 1½ man's length; within this stood two or three houses. There were large fir doors in the palisades with strong clamps; when they were closed, two stout bars were passed through the clamps and thus fastened to them. At the two corners of these … palisades, a high scaffolding is made of fir planks, for a lookout.

In 1604 Tokugawa Ieyasu granted exclusive trading rights with the Ainu to the Matsumae clan; lacking an agricultural base, the domain was dependent on trade; the Ainu in turn became increasingly dependent upon Japanese commodities and prestige goods. Excavated chashi have revealed Japanese lacquerware, ceramics, ironware, and swords, as well as beads perhaps from Sakhalin; consumables included rice, sake, and tobacco. In return the Ainu traded products derived from bird, beast, and fish; plants and medicines; and goods imported via Sakhalin. However, "the market culture of the trading post … destroy[ed] the ecological balance … [through] overhunting and overfishing". By the end of the following century, the depletion of natural stocks resulted in famine. Furthermore, "competition over animals and fisheries was at the heart of most Ainu conflicts".

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