Saturday, April 21, 2018

Maruiwa Castle -Odd castle on oddly rock-

Maruiwa Castle

-Odd castle on oddly rock-



Name: Maruiwa castle (Maruiwa-jo)
Place: Yokokabe Naganohara town, Gunma
Location: 36.52815370507057, 138.6608181762094
Type: Mountain Castle
Built: 16th century
Remaining remnants: Clay walls 

Brief History

Maruiwa castle (丸岩城) is built over Maruiwa mountain, one of about 600 meter height from hillside at the south of current Naganohara town. Naganohara town is located at the end of the long valley of Agatsuma-gawa river, a tributary of Tone-gawa river. Today it works as an entrance to famous spa Kusatsu-Onsen.

Probably as a result of soil, there are many mountains have huge rocks in the western half of current Gunma prefecture, such as Myogi mountain, Iwabitsu mountain or Takeyama mountain. But Maruiwa mountain is an extremely odd one which is a huge round rock vertically stands, like a warhead of missile, and its peak exceeds 1,100 meter from sea level.

Twist of fate

The person who built a castle at such a tough place is unknown, but sometimes said as a local lord Haneo clan. Haneo clan is a descendant of Unno clan which was a traditional spread over from eastern part of Shinano province (Nagano prefecture) to western part of Kozuke province (Gunma prefecture) along with current Route 144. Haneo clan had their main base Haneo castle at about 5 kilometer west from Maruiwa castle, and Maruiwa castle might be their eastern protection.

As Sanada clan which was the lord of Sanada providence in the north part of current Ueda city was a distant relative, when Unno clan was defeated by an alliance of Shingen Takeda (1521-1573), the warlord of Kai province (Yamanashi prefecture) and Yoshikiyo Murakami (1501-1573), the lord of Katsurao castle at the battle of Unnotaira in 1541, Yukitaka Sanada (1513-1574), the leader of Sanada clan, exiled to Kozuke province under coordination of Haneo clan.

Yukitaka married with the daughter of Haneo clan and seek the chance of recovery, but as Yamanouchi Uesugi clan which was the master of Haneo clan did not move, Yukitaka finally left Haneo clan and served to Shingen around 1545. Yukitaka captured Toishi castle from his fatal enemy Yoshikiyo Murakami in 1551 and Yukitaka revived as the lord of Sanada providence under Shingen.

Expansion of Sanada clan

In 1563, Shingen who finished the battle of Kawanakajima against his fatal enemy Kenshin Uesugi (1530-1578) turned his army toward Kozuke province. Utilizing the relation of former Unno clan, Yukitaka Sanada served as a vanguard of Takeda clan utilizing both of his intelligence and armies.

As Saito clan who was the lord of Iwabitsu castle (Gunma prefecture) and master of Haneo clan resisted against Takeda clan, Yukitaka Sanada attacked Iwabitsu castle in 1563. Finally Iwabitsu castle fell by the plot of Yukitaka, and Yukimata Haneo (?-?), the last leader of Haneo clan and father in law of Yukitaka Sanada, died in the battle.

After the fall of Saito clan and Haneo clan, the valley of Agatsuma-gawa river became the territory of Sanada clan. Utilizing Iwabitsu castle as their new main base, Sanada clan gradually expanded their territory toward east, and in 1580, Masayuki Sanada (1547-1611), the next leader of Sanada clan, captured Numata castle (Gunma prefecture) which was an important castle in the north part of Kozuke province.

Closure of Sugao Toge pass

However, after the fall of Takeda clan in 1582 by central ruler Nobunaga Oda (1534-1582) and the death of Nobunaga just after that, utilizing the vacancy of power Sanada clan became an independent warlord. However, Hojo clan which was the warlord of Sagami province (Kanagawa prefecture) which was a former holder of Numata castle and aimed at the capture of all Kanto region suppressed Sanada clan by overwhelming army.

Under such circumstance, it was necessary to prevent the intrusion of Hojo army from the western slope of Haruna mountain to intercept the connection of Iwabitsu castle and Sanada providence from Sugao-Toge pass. Sugao-Toge pass is connected to Takasaki area or Maebashi area which were held by Hojo clan by current Route 406.

As Maruiwa castle existed just at the next of the pass, it was quite suitable to control the traffic of the pass. According to military tales, Yukitaka placed several local lords such as Kamahara clan or Yumoto clan as generals to protect this fort. Posting of this fort might be quite hard because of significant departure from hillside town and no escape route except for main entrance.

Structure of Maruiwa castle

As Maruiwa mountain is a round shaped rock which is encircled by vertical rocks except for its south part connected to backside mountain by saddle point, structure of Maruiwa castle strictly affected by this shape of place. Central area of the castle is a rectangular shaped one of about 20 meter long and 5 meter wide, which might be encircled by clay walls.

Along with the ridge spreads eastward, narrow terraces were built by the edge of the ridge. At the north slope there are several terraces which is not clear if it is artificial or natural, but these terraces might be used as a part of the castle. Hill top area is too narrow and residence of the lord might exist at the hillside of mountain.

At a saddle point which might work as a main gate of this castle ,there is a line of clay wall which prevents both of climbing enemies and strong wind. This area has a flat space and might work as a buffer area both used as a preparation of sortie and receipt of retreat. The impact of natural rock is too large but it has also well made structures, and this shows it was a critical point for Sanada clan.

Abolition after achievement

Hojo clan continuously attempted into the valley of Agatsuma-gawa river to capture Numata castle in the latter half of 1580's, but being separated into Kozuke province and Shinano province, Sanada clan well resisted against the attack of overwhelming Hojo army and kept their territory.

In 1590, after the capture of Nagurumi castle (Gunma prefecture) breaking the treaty, Hojo clan was ruined by central ruler Hideyoshi Toyotomi (1537-1598). Numata castle and the valley of Agatsuma-gawa river was formally held by Sanada clan, and Maruiwa castle lost its tactical value then might be abolished at this time.

Today no building exists but structures of the castle remain on the huge rock. As this mountain is not used as a place of hiking, only quite a few people visit this castle ruin. Both of its location and shape is quite unconventional, but judging from the fact that Hojo clan could not intrude into the valley of Agatsuma-gawa river, Maruiwa castle could work effectively. 


60 minutes walk from JR East Agatsuma-sen line Naganohara-Kusatsuguchi station. 60 minutes drive from Kanetsu Jidoshado Expressway Shibukawa-Ikaho interchange. Entrance of access road is just at the north of Sugao-Toge pass.

Related Castles

Iwabitsu Castle -Strategic base of Sanada clan-
Numata Castle -Respective choice of Sanada family-

Pictures (click to enlarge)

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