The Usui area offers walkers and cyclists the chance to explore the remains of two medieval hill castles、Usui Castle itself, and Moroto Castle on the opposite side of Inba Marsh (the proper Japanese pronunciation is Inba with an ‘n’, but colloquially Imba with a ‘m’ is also widely used), both of which have been preserved as public parks. Today the main road crosses a wide modern bridge between Usui in Sakura City and Moroto in Inzai City; but in the past the only connection was a watashi-bune (ferry or small boat ferrying passengers across the water) running between docks and piers that were built at the base of the steep castle walls.
Medieval castles, usually called yama-jiro in Japanese, were much simpler structures than the huge castles that were built from the late 16th century onwards. The buildings were all of wood, and the earthen walls and moats were made primarily by modifying the existing terrain. The Japanese term literally means ‘mountain-castle’, but in structure and function these local defended enclosures may be closer to iron age and early medieval ‘hillforts’ in the British Isles.
The histories of local battles and the genealogies of Japanese clans are incredibly complicated, and the best an amateur historian can do is try to grasp the general ebb and flood of events. The Usui Clan was a prominent branch family of the medieval regional rulers, the powerful Chiba Clan. The Chiba Clan themselves originated from a lineage of the Heike, the very same clan that established Japan’s first warrior class government, but then lost everything in a disastrous war with their archrivals the Genji Clan.
The Usui Clan is believed to have first constructed their castle sometime in the 12th or 13th century. Muroto Castle across the bay was a defensive enclosure manned by close allies of the Usui lord. Several major battles were fought here over the ensuing centuries, but the fortress was finally decommissioned and abandoned in the early 17th century. Both Usui and Moroto Castles are important historical sites and cultural heritages, preserving dry moats, earthworks and other features typical of medieval hill castles.
臼井城は１２～１３世紀に、千葉氏の一族でた臼井氏によって築かれたと考えあれている。その後、中世を通して数多くの激戦を生き延び、やがて１６０４年、幕府政権の成立とともに廃城となった。現在、一部の城跡は公園として保存されている。印旛沼の向かい側には、臼井城の枝城として築かれた師戸城（もろとじょう）も城跡公園（県立印旛沼公園）としてしっかりと守られている。昔は臼井城と師戸城を結ぶ渡し船があったが、１９６３年に橋が架けられた。
一般的に「城」と言えば、姫路城や小田原城など、ごつい石垣と高い天守を誇る立派な近世城郭のイメージが強い。しかし、このような城の歴史は16世紀の織田信長の安土城から始まり、それ以前の中世山城は在来の地形を生かした土づくり、建物も簡単な木製のものだった。「山城」の英訳について、そのまま直訳すればmountain castle やhill castleになるが、中世のシンプルな山城は、立派な石垣と高い天守を誇るcastleよりも、構想的にも、また機能的にもイギリス諸島のhillfortに近いかもしれない。
下総台地は馬の名産地で、馬に乗って弓を使って戦う技術に長けた坂東武者たちは、平安末期から戦を頻繁に繰り返し、山城を盛んに築いた。山城は見通しの良い台地の縁を選び、スケールは小さいものの、斜面を削ったり、空堀を掘ったりして、敵の侵入を防いだ。残念ながら、殆どの山城は姿を消してしまっているが、空堀や土塁などがはっきりと残る臼井城と師戸城は、貴重な地域文化遺産となっている。
The Tonegawa Zushi was written in 1855, long after Usui Castle had been abandoned. The author describes the immense kusunoki as being on the northwest grounds of the fort ruins, adjacent to a Sanno Shrine. A detailed map is included as well, showing the famous tree at the western edge of the high ground, just behind the Hachiman Shrine. The central set of fortifications, including the honmaru or main keep, are situated to the east. This was probably nothing too fancy, more like a simple wooden structure that also served as the residence of the lord and his family.
This map also shows clearly how the existing topography was put to good use in building the fortifications. The basic topography of the southern Kanto area consists of a fairly simple two-tiered structure. The lower level is the alluvial plain, just a few meters above sea level; while the upper level is a flat plateau-like upland, called daichi in Japanese. The daichi is cut by narrow branching valleys known as yatsu. The daichi is only 20-40 meters high, but the slopes leading up from the plain or valleys are often quite steep.
On the map the steep edges of the daichi appear to have been chiseled back to make them even steeper. In addition, the map shows a toride or detached defensive fortification, probably consisting of wooden walls or barricades of sharpened stakes, just to the southeast of the Hachiman Shrine. The ferry dock connecting Usui with Moroto on the opposite side of the marsh is also indicated.
『利根川図志』が書かれた１８５５年には、臼井城は既に廃城となっていた。しかし、赤松宗旦はこの山城の歴史に深い関心を持ち、その様子を細かく記した地図も描き残してくれた。地図を見ると、本丸は台地の北側の縁に築かれ、有名な大クスは本丸から離れて、台地の西側の縁に位置し、山王社の隣に示されている。
I spent several days walking through the castle ruins and bicycling up and down the narrow farm roads that lace the area. At the Usui Castle Ruins the flat areas that housed the Honmaru and other major structures, as well as the dry moats and inner walls, can be explored readily on foot. The Narita Kaido, the old pilgrimage road leading from Edo to the famous Shinshoji Temple at Narita, passed just south of the castle ruins. Weathered stone signposts still mark the original route.
臼井城址公園は空堀や崖がはっきりと残っており、中世の山城の構想を知ることができる。公園周辺の細い農道をチャリで走り廻って、天満宮や千葉氏の氏神である妙見社を訪ねた。しかし、城の土塁を成していた斜面は特に険しい坂道として残っており、ぼくの脚力とスタミナにはぎりぎりだった。成田街道の旧道は城址公園の南側を通っていた。多くの道標も残って、歴史ファンをわくわくさせる。
Unfortunately, the area to the west, where the famous kusunoki stood, has been developed as a single-family housing complex; and nothing at all remains of either the Sanno Shrine or the huge kusunoki. This was a great disappointment. The tree depicted in the Tonegawa Zushi was easily big and old enough to house several kodama. In fact, according to local folklore a large snake once lived in a cavity formed near the base of the tree trunk. This snake is said to have occasionally come crawling out to dine on the local populace.
The old tree is believed to have been weakened by unusually heavy snows, and begun dying in the 1860s, just a few years after being described in the Tonegawa Zushi. I did, however, come across several huge kusunoki in the sacred grove surrounding the Hachiman Shrine, including the trunk of one dead tree that must once have been a truly spectacular specimen. This second tree is also described in the Zushi, and noted to have a girth of about three jo, or about 15m. A shimenawa twisted rope, decorated with zigzag strips of white paper, marks this tree as a goshinboku, a tree designated as especially sacred to the enshrined kami.
台地の西側で山王社と『利根川図志』の挿絵に描かれた大クスを探してみたが、残念ながら住宅開発が進み、現在はその姿を見ることができない。しかし、臼井の総鎮守とされる八幡社の社寺林には、クスノキだけではなく、スダジイなどの巨木も多く聳え立っている。特に圧倒されるのは、社殿の脇に立っている大クス。この木は枯れてしまったが、根幹が残っており、神社のご神木として大事に保存されている。枯れ木ではあるものの、その神秘的な力強い佇まいは今なお感じられる。『利根川図志』には、幹回り5丈の大クスと別に、八幡宮の脇に聳え立つ幹回り３丈（約９ｍ）のクスノキ巨木についての記事もある。おそらく、現在のご神木はこの3丈の木の残りであろう。
The whole Usui area, though heavily developed as a residential district, is still home to an unusually large number of huge old trees. One possible clue to the origin of these trees comes in the form of a local legend. According to this story, in 1333 the then lord of the Usui Clan passed away at the young age of 25, leaving behind his three year old son Takewakamaru. Care of Takewaka was entrusted to the lord’s younger brother, who was to watch over him until he grew old enough to take over clan leadership. But the younger brother’s mind became poisoned by greed. He hatched a plot to kill the young boy, and take over the lordship for himself.
Otatsu, the boy’s nursemaid, caught wind of the plot, and with the help of sympathetic relatives managed to sneak the boy out and send him to a Zen temple in Kamakura. The Uncle was enraged when he discovered Takewaka missing, and soon realized that Otatsu was involved. Pursued by soldiers, Otatsu fled and hid herself in the dense reed beds around the water’s edge. She was well hidden, but with the poorest timing managed to let out a soft cough just as the soldiers were passing by. Otatsu was discovered and executed on the spot.
Later, as the story of Otatsu’s heroism became known, her spirit became revered as a sort of local saint. In a strange twist of fate, Otatsu, who died because of a single untimely cough, took on the role of a spirit who could help cure coughs and colds. Her grave is situated in a small shaded park near the banks of Inba Marsh. According to local custom, people with coughs or sore throats can get relief by leaving cans or bottles of tea at the grave. Similarly structured folklore stories, in which a person gets caught due to an untimely cough then later becomes a special guardian spirit able to help cure colds and throat illnesses, are told at various other spots in the Hokuso area.
Otatsu is the heroine of the story, but the account does not end with her death. Takewaka grew to manhood at the Zen temple, then entered the service of the shogun Takauji Ashikaga. He served faithfully in the Kyushu campaign, and returned a seasoned and skillful samurai warrior. Changing his name to Okitane Usui, he took back Usui Castle from his brother, who was eventually forced to commit seppuku or ritual suicide.
According to legend, while on campaign in Kyushu, Okitane was helped to victory by the blessings of the great Hachiman Jingu shrine, located at Usa in what is now Hyuga Prefecture. In gratitude, he founded the Usui branch Hachiman Shrine (The kami energy of a main Shinto shrine can be can shared out to new branch shrines without losing any of its original strength). He also founded a branch of the Tenmangu Shrine, headquartered at Dazaifu n Kyushu; as well as several Zen temples in honor of the monks who took such good care of him as a boy.
According to legend, Okitane also brought back some cuttings from the famous sacred kusunoki trees growing at the Usa Hachiman Jingu, which he planted around the Hachiman Shrine. The biggest of these is the immense trunk currently serving as goshinboku.
八幡宮のご神木は、臼井地区に伝わる『おたつの伝説』に深く結びついている。この伝説によれば、１３１４年、臼井城の城主であった臼井佑胤（すけたね）は、わずか２５歳の若さで亡くなり、その際に３歳の幼い息子、竹若丸を残した。竹若丸の後見は佑胤の弟である胤氏（たねうじ）に託されたが、胤氏は子どもを殺して臼井城を乗っ取ろうと企んだ。しかし幸い、竹若丸の乳母、阿多津（おたつ）はこの陰謀を嗅ぎつけて、忠実な親戚と手を組んで竹若丸を城から脱出させ、鎌倉の禅宗の寺に預けた。
竹若丸の脱走に気づいた胤氏は、その作戦に関与した阿多津に激怒した。阿多津は必至に逃げて、水辺のヨシ原の中に身を隠したが、あいにく咳が出てしまい、追手に発見され、その場で処刑された。鎌倉に逃れた竹若丸は成長し、足利尊氏（あしかがたかうじ）に従って、九州の戦で立派な武功を挙げた。戦後、臼井に戻ってきて名を臼井興胤（おきたね）に改めた後、１３４０年頃に臼井城を取り戻した。
興胤は九州の軍事作戦の祭、宇佐八幡宮（大分県）と太宰府天満宮（福岡県）に武運を祈って、その加護によって戦勝を果たしたと考えた。そのお礼として、臼井に八幡社と天満宮を建てたという。また、宇佐八幡宮から持って帰った神霊クスノキの小枝を地面に刺し込んだところ、これは根付いて、現在の八幡社のご神木に成長したと伝えられている。
若い竹若丸に忠実に仕えて命を落とした阿多津の話は、村人の心に深く響いた。そして、江戸時代中期には、村人たちが処刑された場所に祠を建立して、「おたつ様」として拝んだ。不思議なことに、咳を出して命を落とした阿多津は、逆に咳を治してくれる「咳神」として祭るようになった。「おたつ様」の祠は現在も残っており、お茶を備えてお願いすると風邪や咳が治ると言われている。似たような伝説は、北総の各地で語り継がれている。
