According to the entry in the Nihonshoki in the section of 22nd March, the 2nd year of Taika (646) (in the old calendar), after the Taika Reforms the Taika Hakusorei (the Taika funerary law) was stipulated, as a result of which the construction of Zenpo-koen-fun (the front-square and rear-round tomb mounds) was stopped and the downsized kofun were increased.
『書記』大化2年（646年）3月22日条によれば、大化の改新の後に大化薄葬令が規定され前方後円墳の造営が停止され古墳の小型化が進む。