Among various archeological monuments in the territory of Japan and the Russian Far East there is a special category of settlements possessing attributes of natural and/or artificial fortification. Japanese researchers use the term “Chasi” for the given type of site identification. This is an Ainu word designating a fortress, or fortified area. At this time there are more than 500 Chasi identified in the northern part of the Japanese archipelago, some of them are studied by means of archeological excavations. About 20 sites of the Chasi type were found on Sakhalin. Until recently, Chasi sites were known only from literary and cartographical sources on the Kurile Islands.

As a result of archeological field surveys, which have been carried out on Kunashir Island in 2001-2003 by the authors of this article, 11 archaeological sites with attributes of both natural and artificial fortification were discovered, and eight of them were identified as Chasi, as mentioned in Russian and Japanese written sources of the 18-20th centuries. All settlements are located along the seacoast. Six sites were discovered on the northwest (Okhotsk) coast of Kunashir, and five on the southeast (Pacific) coast. It is obvious, that ancient inhabitants of the sites aspired to use to the full extent some feature of relief and topography of the island. They used abrupt slopes, high steep coast, and narrow ridged spurs as natural factors of protection of the settlements. As a rule, they were supplemented with artificial elements of fortification, such as moats and (less often) earth mounds.

The wide variability of the “Chasi” type of sites, along with their low level of scrutiny suggests different cultural and chronological associations, and probably various purposes. The few archaeological artifacts collected from pit testing of some of the Chasi sites on Kunashir, correspond to the final stage of the Okhotsk Culture, and the early period of Ainu cultures (10-13th centuries A.D.).