Komoro Castle

Komoro Castle, located in Komoro City, Nagano Prefecture, is a historically rich castle ruin known by several poetic nicknames such as “Suigetsu-jō” (Drunken Moon Castle), “Ana-jō” (Underground Castle), and “Hakutsuru-jō” (White Crane Castle). The name “Ana-jō” reflects the castle's rare structural feature — its grounds are situated lower than the surrounding town, giving it the appearance of being hidden underground.

The castle’s origins date back to 1487 (Chōkyō 1), traditionally attributed to Mitsutada Ōi. During the Warring States period, the famous warlord Takeda Shingen significantly renovated the castle to strengthen his hold over the Eastern Shinano region. While it's said that the basic layout was designed by his strategist Yamamoto Kansuke, no definitive historical evidence confirms this.

Komoro Castle was fully developed into an early-modern Japanese castle during the Azuchi–Momoyama to early Edo periods, with Sengoku Hidehisa playing the key role in its transformation. He reinforced the stone walls, built a three-story tenshu (main keep), and used gold-leaf tiles featuring the paulownia crest, showcasing the lord’s authority. Unfortunately, the tenshu was destroyed by lightning in 1626 (Kanei 3) and was never rebuilt.

What sets Komoro Castle apart is its lower elevation than the town around it, making it one of Japan’s rare “sunken castles”, in contrast to most castles built on elevated terrain. The western side is protected by the steep cliffs of the Chikuma River, while the northern side utilizes volcanic terrain and ravines formed by nearby Mount Asama as natural moats — a unique combination of natural and artificial defenses.

Today, the castle ruins are preserved as “Kaikoen” (Kaiko Park), featuring stone walls, gates, and moats, surrounded by cherry blossoms, autumn foliage, and a poetic natural atmosphere. The park also includes a museum and zoo, making it Komoro’s most iconic sightseeing spot.