When sekke (line of regents and advisers) were established among court nobles starting at the end of the Heian period, and the social status and family status became fixed, the so called genpeitokitsu, or the Minamoto clan, Taira clan, Fujiwara clan, and Tachibana clan, became the only four family names allowed to become kugyo (Later, the Sugawara clan, Abe clan, and Kamo clan were allowed, but limited to those in the lineage of eldest son).
平安時代末期より公家の中で摂家が確立するに至り、貴族の格式、家格が固まってくると公卿になれるのは源氏・平氏・藤原氏・橘氏のいわゆる源平藤橘の四姓だけになった（後に菅原氏・阿倍氏・賀茂氏なども嫡流に限って認められた）。