Okamoto Castle (Awa) -History of peninsular brave (10) retreat and restructuring-

Okamoto Castle (Awa)

-History of peninsular brave (10) retreat and restructuring-

Overview

Name: Okamoto castle (Okamoto-jo)
Alias:
Place: Tomiura-cho Minami-Boso city, Chiba
Type: Mountain Castle
Built: 16th century
Remaining remnants: Stone walls, clay walls and moats
Title:

Brief History

Continued from Part 9

Okamoto castle (岡本城) is located on a hill of 60 meter height from hillside at the north of Tomiura town. Tomiura area is just the north from Tateyama plain, and is a natural good port protected by cape Taibusa.

Even though not so large area, but being protected by sea, river and hills, it is a suitable place to have a main base. Beside, this area is exactly at the exit of Tokyo bay thus an important place to control marine transportation. At the tip of Cape Taibusa, ruin of former military base still remain.

Origin of Okamoto castle

Precise year is unknown but Okamoto castle was built around 1570 by Satomi clan, as a base of its navy. Satomi clan was a traditional clan which was a branch house of Nitta clan, a major house of Minamoto family and rival of Ashikaga clan, which established Muromachi Shogunate. Precise situation is unknown but Satomi clan landed Awa province (south half of Boso peninsula) in the latter half of 15th century under the order of Ashikaga clan, same as Mariyatsu Takeda clan.

Soon Satomi clan gathered local naval clan and seized Awa province beating existing local lords in 20 years from their main base Inamura castle. At the time of Yoshimichi Satomi (?-?), Satomi clan started to expanded to east part of Kazusa province, and gained Masaki clan, a powerful local lord of the area, as their retainer.

But after the death of Yoshimichi, there arose an internal conflict named "Tenbun no Naikou" (conflict in Tenbun period) in 1534, and Yoshitaka Satomi (1507-1574), born as side line of the clan, ruined Yoshitoyo Satomi (?-1534), the head of main family and gained the leader position under support of Hojo clan, the fatal rival of Satomi clan.

Struggle of Satomi clan against Hojo clan

However, after the seizure of leader position, Yoshitaka Satomi broke with Hojo clan. Just at time the first battle of Konodai occurred at current Ichikawa city, between Hojo clan and an alliance of Ashikaga clan, Mariyatsu clan and Satomi clan. The alliance lost the battle then leader of Ashikaga clan died and Mariyatsu clan also get confused. But Yoshitaka left the battlefield without damage, then ruined weakened Mariyatsu clan and seized whole Kazusa province.

Yoshitaka Satomi who captured Kazusa province next aimed at Shimousa province (root of Boso peninsula and western part of Chiba prefecture) from his main base Kururi castle (Chiba prefecture). But Hojo clan which already captured Musashi province (Tokyo metropolis and Saitama prefecture) also seek Shimousa province, thus both clan fiercely fought for Shimousa province and Kazusa province.

Hojo clan had significantly larger territory and soldiers, thus sometimes broke Satomi army and once attacked Kururi castle, the main base of Satomi clan. But Yoshitaka cooperated with external powers such as Kenshin Uesugi (1530-1578), the fatal rival of Hojo clan, then made counter attack to Hojo clan and well kept the territory.

Retreat and restructuring of Satomi clan

But in 1574, Yoshitaka Satomi who was the backbone of Satomi clan died in ill. Kenshin Uesugi lost its territory in Kanto region thus could not help Satomi clan any more, and Hojo clan organized local lords at border area. Looking at this situation, Yoshihiro Satomi (1530-1578), son of Yoshitaka Satomi, finally made peace with Hojo clan in 1574. This was subordination of Satomi clan to Hojo clan, and Satomi clan lost north half of Kazusa province.

Furthermore, soon Yoshihiro also died in ill, and an internal conflict occurred between his son Yoshishige Satomi (1570-1622) at Kururi castle and his younger brother Yoshiyori Satomi (1543-1587). Yoshishige cooperated with Masaki clan, the important retainer of Satomi clan had strong army, but Yoshiyori broke them under support from Hojo clan. Yoshiyori forced Yoshishige to be a priest and purged Masaki clan.

Yoshiyori Satomi somehow united Satomi clan again but the situation was bad. There is no room for territorial expansion before Hojo clan, and Satomi clan lost military power during internal conflict. After a long campaign there was also a fiscal problem, and even though made peace Satomi clan needed power to avoid complete surrender to Hojo clan.

Among such situation, Yoshiyori Satomi tried to gain power by improving commerce and marine transportation. Originally Satomi clan had a strong navy activated at Boso area, and its location is a connecting point of inner gulf transportation and external shipping. Satomi clan moved their main base from inland Kururi castle to bayside Tomiura area, and used Okamoto castle as its main base.

Structure of Okamoto castle

Okamoto castle spreads over a hill of 500 meter long and 200 meter width like oblong "U" letter. The central area is a flat area of 50 meter long and 20 meter width at the western part of the hill, and there might be a watchtower building. At the middle of the castle there is a small peak having small stone wall at its slope, and it is said that this place is used to confine Yoshishige Satomi. There is another large area at the east of the castle, and main gate with stone wall might exist here. Many terraces are built at the slope surrounding these core areas.

Different from Kururi castle or other castles in Kazusa province which had long and narrow path all over the hill like a neuron, Okamoto castle has a ordinary shape of mountain castle that have layers of terraces by digging slopes. Originally Satomi clan built this type castles such as Inamura castle or Shirahama castle at first stage, and Okamoto castles returned to this shape.

It might be necessary to show the authority of the lord by placing residence on the mountain, and it was necessary to respond to the change of battle based on the spread of matchlock guns. Considering increase of fire power, narrow paths might be broken easily than attack of matchlock gunners. But at the east edge of the hill, traditional style of narrow line partially remains. Even though far small than Kururi castle, including its location, efforts of restructuring is seen at Okamoto castle.

Survival under Toyotomi government

Under Yoshiyori Satomi, Satomi clan gradually recovered its power under commerce and marine transportation. In 1580, as situation became improved, Yoshiyori built Tateyama castle, to place the center of commerce at more wider area. Satomi clan kept relationship with both of Hojo clan and anti-Hojo lords, and seek for next chance.

In 1590, central ruler Hideyoshi Toyotomi (1537-1598) sent a overwhelming army to ruin Hojo clan. Satomi clan already connected to Hideyoshi, and sent their army to capture former territory deprived by Hojo clan. But Yoshiyasu Satomi (1573-1603), son of Yoshiyori, lacked coordination with Toyotomi general and arbitrarily administrated occupied area, and invoked anger of Hideyoshi. As a result, south part of Kazusa province was confiscated thus Satomi clan kept only Awa province.

Anyway Satomi clan once survived as a feudal lord under Toyotomi government. In 1591, Yoshiyasu Satomi moved his main base from Okamoto castle to Tateyama castle (Chiba prefecture), to show the restart of Satomi clan reflecting the decrease of territory. Okamoto castle might be abolished at this time.

Afterward of castle

Today no building is left and major part of the castle become agricultural field. But terraces of the castle still keeps its shape, along with small stone wall. Compared with huge mountain castles such as Kururi castle or Otaki castle, the decision of Satomi clan to change from land power to sea power is clearly seen. Looking at blue sea, curved beach and Cape Taibusa, a short-term quiet after terrible storm Satomi clan might experienced is felt.

Continue to Part 11

Access

20 minutes walk from JR East Uchibo line Tomiura station. 10 minutes drive from Futtsu-Tateyama Expressway Tomiura interchange. There is no parking near castle and it is necessary to park at Tomiura station or Tomiura beach.