Koizumi Castle

Koizumi Castle is a medieval Japanese fortress built on a 33-meter (108-foot) high plateau in the flat terrain of Gunma Prefecture. The site contains multiple moats, earthen ramparts, and defensive walls that outline the original fortification structure and are now part of Shironouchi Park.

The fortress was founded in 1489 by Tomimochi, son of Yuki Mochitomo, and passed between several feudal lords over the following century. It fell to Toyotomi Hideyoshi's forces in 1590, ending its role as an active military stronghold.

The castle grounds hold relocated burial mounds from the Kofun period, protected as important cultural properties by Oizumi municipal authorities. These archaeological remains show how this location was inhabited and used across many centuries.

The former castle site is now a public park with clear moat and rampart features that are easy to explore on foot. The terrain can be uneven, so sturdy walking shoes are helpful for navigating the grounds.

Oval stone pillars engraved with the word Koshin stand between the inner and outer moats, offering evidence of Edo period religious rituals performed at the site. These markers represent personal spiritual practices that visitors can still observe today.