The Kawachi-Otsuka Tumulus (part of the Otsuka Tomb Reference Site) is a keyhole-shaped burial mound. The mound is 335 meters long, 185 meters in diameter at the circular portion, 230 meters wide at the triangular portion, and is surrounded by a moat that varies from 35 to 70 meters. Boasting the 5th largest construction among tumulus tombs across the country, the mound is thought to represent the final stage in keyhole-shaped mound construction, which changed with the eras. Dating for the mound puts it at somewhere between the mid and late 5th century A.D. At present, the mound is divided in half east to west, straddling the border between Otsuka in Matsubara City and Eganosho in Habikino City.