Akatsuka Castle, Medieval castle ruins in Itabashi, Japan

Akatsuka Castle is a medieval hillfort whose honmaru stood on the northeastern edge of the Musashino plateau, above the wetland of Tokumarugahara. The site keeps more earthworks than any other castle ruin in Tokyo's 23 wards apart from Edo Castle: earthen ramparts, dry moats, a water moat, a moat cut and steep scarps. A stone monument marks the honmaru on the small hill, and the former inner moat below serves as the Akatsuka Tameike pond.

The fortress was founded in 1456 and served as a stronghold for the Chiba family in the Musashi region. It was abandoned in 1590 when major military changes restructured local power throughout the area.

The name Akatsuka comes from the Akatsuka district, where the Chiba brothers Munesane and Yoritane settled after fleeing the Chiba clan's internal conflict. The site is now part of Akatsuka Park, whose plum grove hosts the Akatsuka Plum Festival in early March each year, and the adjacent Akatsuka Tameike Park pond, once the castle's inner moat, is used for fishing.

The site is reachable on foot from Nishi-Takashimadaira Station or Narimasu Station, requiring a walk of roughly 15 to 20 minutes from either location. The ruins sit within a public park that is freely accessible and suited for a casual visit.

The fortress controlled two critical transportation routes: the river crossing at the Arakawa and the road connecting the northern and southern parts of the Musashi region. This strategic location made it a key point for commerce and administration of the area.