The Akatsuka Tumulus is a keyhole-shaped tumulus, about 58-meters long, located on Takamori-no-dai hill in Usa City, Oita Prefecture. It is one of the oldest tumuli in the Kyushu region. It was excavated in 1921. From the stone coffin located at the center of the round chamber, five mirrors, cylindrical beads, and fragments of iron swords were discovered. These mirrors, decorated with triangular rims and motifs of animals and gods, were made in China. Other examples produced from the same mold have been found in the Ishizukayama Tumulus in Fukuoka Prefecture and the Tsubai Otsukayama Tumulus in Kyoto Prefecture.