These burial mounds are thought to be the resting places of successive generations of Yoshinogari rulers. These are artificial mounds piled in layers of different kinds of soil and very strong in structure. 14 burial jars were found in the mounds; one of them kept glass beads and an elaborate-designed bronze sword. These burial mounds were made and used in the middle Yayoi period, 1 B.C. But they were not used as tombs afterward, and it is believed to have been a resting place of ancestral spirits.