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This article is in the series Walking the Japanese Castles
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Komoro Castle (小諸城, Komoro-jō) is a hirayama-style castle located in Komoro, central Nagano Prefecture. It is unique as it is situated lower than the surrounding castle town. Komoro Castle is therefore known as Ana-jō (穴城, "Hole Castle").

Komoro Castle (小諸城)

The lowland along Chikuma River was fortified land with several deep valleys running by the side of the highway. On the map below, it is visible that the west side of Sannomon (三の門, third gate) forms a triangular plateau. The Sannomaru (三の丸, third bailey) was set up on the east side of Sannomon to strengthen the defences of the castle.

Komoro Castle (小諸城)

The map was based on GSI Map powered by the Geospatial Information Authority of Japan. The location of enclosures is estimated.

The history of the castle started when Kiso no Yoshinaka (木曾義仲, 1154-1184), the son of Minamoto no Yoshikata and rival of his cousin Minamoto no Yoritomo in the Genpei War (1180-1185), constructed fortifications on the east side of the present-day castle ruins. In the first year of the Chōkyō era (1487), warlord Ōi Mitsutada (大井光忠) built Nabebuta Castle (鍋蓋城) north of Ōtemon (大手門) and established a castle within the limits of the second bailey (二の丸 ninomaru).

When Takeda Shingen invaded Shinano in 1554, he understood the strategic importance of the area, which formed a corridor connecting the Saku and Ueda basins. He ordered his chief strategists Yamamoto Kansuke (山本勘助, 1501-1561) and Baba Nobufusa (馬場信房, 1514-1575), both members of Shingen's "Twenty-Four Generals", to build Komoro Castle. When the Takeda were defeated by Oda Nobunaga in 1582, the castle was handed over to Takigawa Kazumasu (滝川一益, 1525-1586), one of Oda's retainers. After a brief interlude when the Late Hōjō controlled the region, Tokugawa Ieyasu made Sengoku Hidehisa (仙石秀久, 1552-1614) the first daimyō of the Komoro Domain (50,000 koku) in 1603. Hidehisa and his son Tadamasa reinforced the walls and improved the structure of Komoro Castle, the surrounding castle town and roads. After Tadamasa was transferred to Ueda Domain, several daimyō followed: the Hisamatsu branch of the Matsudaira (1624-1648), the Aoyama (1648-1662), the Sakai (1662-1679), the Nishio (1679-1682), and the Ishikawa (1682-1702). In 1702, the domain was transferred to a branch of the Makino clan who held Komoro for ten generations until the beginning of the Meiji Period.

Although the main castle ruins are located in the Kaikoen (懐古園) garden west of Sannomon, we recommend that you visit the main gate opposite the railroad tracks.

① Ote Gate (an Important Cultural Property) built by Sengoku Hidehisa in 1612. In the Meiji Period, it was used as a restaurant and a private school. After a complete renovation, it was restored to its original state in the Edo era.

Komoro Castle (小諸城)

② The Sannomon (三の門), another Important Cultural Property. The panel above the entrance says "Kaikoen" (懐古園). It was destroyed in a flood in 1742.

As this gate located on the peak of the triangular plateau was well-guarded, the enemy had no other chance than to scale the cliffs around the castle.

Komoro Castle (小諸城)

A masugata (桝形) along the path between Sannomon and the Ninomaru. Masugata are squares enclosed by earthen embankments, stone walls, moats or gates used to protect a castle entrance.

Komoro Castle (小諸城)

③ The stairs leading to the Ninomaru (second enclosure). There aren't any noteworthy remains in the enclosure.

Komoro Castle (小諸城)

④ The stairs to the southern enclosure.

Komoro Castle (小諸城)

⑤ An archery ground in the northern enclosure.

Komoro Castle (小諸城)

⑥ Kuromon Bridge (黒門橋) built over Momiji Valley (紅葉谷 Momijidani) located between the main and the second enclosure. The valley is, in fact, a dry moat (堀切 horikiri).

Komoro Castle (小諸城)

⑦ The restored arsenal.

Komoro Castle (小諸城)

⑧ Jigokudani (地獄谷, "Hell Valley") at the northern side of the castle. The cliff carved into the plateau was formed of volcanic ashes from Mount Asama is very brittle.

Komoro Castle (小諸城)

⑨ The view of Chikuma River from Mizunote Observatory (水の手展望台). Right under observatory is an akazumon (不開門, lit. "closed gate"), a secret gate said to be an escape route in times of emergency.

Komoro Castle (小諸城)

⑩ This is the valley at the southeastern side. Though it has no specific name, it is as deep as Jigokudani. The other side of the valley is a zoological garden.

Komoro Castle (小諸城)

⑪ The base of the castle tower is in the corner of the main enclosure (本丸 honmaru). In 1626, the three-storey structure was struck by lightning and burned out. It was never rebuilt.

Komoro Castle (小諸城)

⑫ The stone wall around the honmaru. There are no handrails to prevent visitors from slipping and falling.

Komoro Castle (小諸城)

Rough and weathered stone walls and stairs create an atmosphere appropriate for the name "Nostalgia Garden" (懐古園 Kaikoen).

Komoro Castle (小諸城)

Komoro Castle (小諸城)

In 2006, Komoro Castle was listed as one of the 100 Fine Castles of Japan by the Japan Castle Foundation.

Date of visit: 13 October 2013


  • Address: Tei, Komoro-shi, Nagano
  • Transport: A 5-minute walk from Shinano Railway Line Komoro Station
    3km from Joshinetsu Expressway Komoro Interchange via Prefectural Route 79
  • Parking: Kaiko-en / Main-Gate Parking (charge: Spot 'P' pointed on the above map)
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Hiroto Uehara
Hiroto is an ordinary Japanese office worker, but his true mission is searching for castles on the weekend.


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