In the Heian period, the system changed from "one county one kiln" to "one country one kiln" in western Japan where Sueki production was active, which led decrease in production areas.
平安時代には、これまで須恵器生産が盛んだった西日本で一郡一窯の体制から一国一窯への収斂がみられ、産地の数が減る傾向がでてきた。