Kawachi Otsuka Tumulus (Otsuka Mausoleum reference site) is a keyhole-shaped tumulus. The length of the mound is approximately 335 meters, the circular rear portion is approximately 185 meters, the front portion is approximately 230 meters wide, and it has a moat that is 35 to 70 meters wide. It is the fifth largest mound in Japan, and is said to be the final stage of the keyhole-shaped tumulus, which changed its shape over time. It is said to date from the late 5th century to the end of the 5th century. The tumulus straddles Nishi-Otsuka in Matsubara City and Eganosho in Habikino City, dividing the area into east and west.