In the aristocratic society family lineage which allowed one to ascend to Kugyo (the top court officials) began to be limited since the late Heian period, and as kakaku (family status) was fixed when Sekke (line of regents and advisers) was established by the Northern House of the Fujiwara clan, a hierarchical kuge society was formed by the early Kamakura period.
平安時代末期ごろから貴族社会において公卿に昇る家柄が限定されるようになり、藤原北家による摂家の確立に伴って家格が固定化し、鎌倉時代前期ごろまでに公家社会が形成された。