The Kosai Kiln Site Group is a group of old kiln sites located in Kosai and Arai-cho, Hamana-gun, Shizuoka Prefecture. The kiln sites are located on the valley slopes of Takashiyama Hill, which occupies a corner of the southwestern shore of Lake Hamana. The Takashiyama Hills are the easternmost part of a broad area of Pleistocene hills that includes Takashibaru and Tenpakuhara in Toyohashi City, Aichi Prefecture, and Shindokuhara in Kosai Town, Hamana County.
The Takashiyama Hills are covered with a layer of soil called the Washizu Mud Formation, which contains a fine white clay. This white clay is mainly composed of feldspar and contains quartz and other elements, but has low iron content, making it particularly suitable for use as pottery clay. The Kosai Kogan Site Group has discovered approximately 200 kiln sites so far, and the period of existence of the kiln sites is extremely long, ranging from the late Kofun period (early 6th century) to the Kamakura period (13th to 4th centuries). Of these, only a few Sue ware kiln sites belong to the Kofun period, and they flourished most during the Nara and Heian periods.
There are also dozens of mountain tea bowl kiln sites dating from the late Heian to Kamakura periods. The types of products found at the Kosai kiln sites are mainly containers such as lids, cups, bowls, plates, vessels, jars, tall cups, suribachi, and steamer, and it is evident that the types of vessels have changed over the ages. It is also interesting to note that this kiln site is located near Lake Hamana, where pottery weights, a type of fishing tool, were produced.
In addition, ceramic horses, inkstones, jars and vessels with animal feet were also found. The structure of the kiln was basically in the form of a cellar kiln throughout the entire period, although some partial modifications were made during the period.
