Chausuyama Kofun, Keyhole-shaped burial mound in Tennōji Park, Japan

Chausuyama Kofun is a keyhole-shaped mound in Tennoji Park, with a circular rear section and a rectangular front section. It is about 26 meters above sea level, and the park's paths run around and over it. A pond called Kawazoko-ike lies between the mound and the rest of the park.

Built in the 5th century for a local chieftain, this is one of the largest keyhole-shaped tombs in Osaka, though the person buried there is unknown. In 1546, Yamanaka Matazaburō, a retainer of Hosokawa Harumoto, built Ōtsuka Castle on the rear circular mound. During the 1614 winter siege of Osaka, Tokugawa Ieyasu set up his headquarters here, and in the 1615 summer siege, Sanada Nobushige (Yukimura) used it as his base for the Battle of Chausuyama.

The mound is also called Araraka or Ararakayama, and a stone coffin lid said to have been dug from it is kept at Shitenno-ji. In 1614 it served as Tokugawa Ieyasu's headquarters, and in 1615 as Sanada Nobushige's, during the Battles of Osaka.

You can reach the mound through the adjacent park, which has pathways allowing you to explore the structure. Informational markers are placed around the site, making it easy to understand what you are seeing without advance preparation.

The mound's 26-metre summit counts among Osaka's five lowest mountains, as recorded by the Geospatial Information Authority benchmark. In 1546 the rear circular section carried Otsuka Castle, built by Yamanaka Matazaburo, a retainer of Hosokawa Harumoto.