The Hazamiyama tumulus, whose front part faces the east, is considered having been constructed in the middle era of the fifth century, while the Nonaka Miyayama tumulus, whose front part faces the west, is considered having been built in the first half of the fifth century.
はざみ山古墳は前方部が東を向き、5世紀中葉の造営年代が推定されるのに対し、野中宮山古墳は前方部が西を向き、5世紀前葉に造られたと考えられる。