Written with the intention of being a successor to the Six National Histories, it covers approximately 200 years, the reigns of 15 emperors from that of Emperor Uda up to February 1092 during the reign of Emperor Horikawa, when the Regency government was weakening.
六国史の後継たるべく宇多天皇の治世から起筆し、摂関政治権力の弱体化した堀河天皇の寛治6年2月（1092年）まで、15代約200年間の時代を扱う。