外堀の土塁 The Structure of the Outer Moat Ground 外堀土塁の構造 The Structure of the Base 牛込門から赤坂門までの江戸城外堀は、谷地形を利用し、広い堀幅の水面と、水面から高い土塁を持つ江戸城防御のための空間で構成されています。目の前に見える土手もその土塁の一部であり、2013（平成25）年から始まった石垣修復工事、その後のJR飯田橋駅西口駅舎等の工事に併せ調査が行われ、桝形石垣付近は江戸時代当時の規模を目安とした土塁の復元をしています。 外堀の土塁は、厚さ５～10cm程度ごとに土や粘土、砂など様々な種類の土を積み重ねて突き固められた版築と呼ばれる技法で作られています。地層断面をみると、土手の斜面方向とは逆に、水面の方に向かって地層が上がっています。これは、土砂崩れを防ぐためと考えられています。土塁の道路端には土留めの石垣が築かれていましたが、現在では土手に沿って通る道路の端に確認できる通り、コンクリートの小型擁壁に代わっています。
The section of Edo Castle’s outer moat between Ushigome and Akasaka Gates was constructed by utilizing the valley topography, which allowed for the development of a wide canal surface and tall earthwork fortifications. The embankment visible here formed a portion of the area’s earthen fortifications. In 2013, a series of excavations were carried out in conjunction with a project to repair the stone walls and redevelop the western side of JR Iidabashi Station. The project enabled the reconstruction of earthen fortifications on the same scale as those that existed in the Edo era. As a result, contemporary visitors to the site can experience the grand scale of the historical fortifications that existed in the area. The outer moat’s fortifications were constructed using a rammed-earth technique in which 5-to-10-centimeter layers of earth and clay were stacked on top of one another and tamped down. An examination of the fortifications geological profile reveals that the layers of earth and clay rise towards the towards the moat’s surface and away from the embankment slope, It is likely that this construction method was utilized in order to prevent landslides. Earth-reinforced stone walls were constructed along the roadside lining the earthen fortifications. However, as can be determined from the roadside currently located parallel to the embankment, the original earth-reinforced walls have been replaced by small-scale concrete retaining walls.
外堀土塁の水際部分（発見された水際石垣） Waterside Part of The Outer Moat Ground (Discovered Waterside Stone Wall 2015（平成27）年に行われた発掘調査の結果、外堀の水際には、土手が崩れないようにするための低い石垣が作られていたことが判明しました。発見された場所は、牛込橋から140m程度市谷方向に進む地点の線路の間で、石垣の基礎部分と考えられる 1〜2段の石積みが、外堀で初めて確認されました。この石垣は、明治期に甲武鉄道が敷設された際に、上段部分が撤去され、基礎部分はそのまま埋められたものと考えられます。
An archaeological excavation carried out in 2015 revealed the existence of low stone walls along the moat’s edge. They were likely constructed in order to prevent the embankment from collapsing into the moat. The site where the walls were discovered is located in a section of rail track approximately 140 meters away from Ushigome-bashi Bridge in the direction of Ichigaya. At that site, excavators found one- and two-tier layers of stone, which are thought to have comprised the stone walls’ structural foundation. When the Kōbu Railway was constructed in the Meiji period, it is thought that the upper portion of the stone walls were removed and the foundation was buried.
外堀土塁の植栽 Planting of The Outer Moat Earth Fence 1636（寛永13）年、外堀土塁が完成すると、幕府は翌年、堀方七組の東国大名に命じて、土塁上部から2.7m程下がった位置に、一間（約1.8m）間隔で大きめの松杉を、その内側には小さめの苗木を、二筋にわたって植樹させました。植木奉行（のち普請奉行）の管理下に置かれた牛込土橋～筋違橋の土手と堀は、近辺に屋敷を拝領する武家に割振り、植木の手入れと草刈りを担当させました。幕末に日本を訪れたオイレンブルクの『日本遠征記』によれば、「城壁天端の平坦部とその内側にはモミなどの針葉がぎっしりと並び、水面には何千という野鴨が住み着いている」と記されています。なお、真田濠（現上智大学グラウンド）の土塁上には、往時の姿を思い浮かべることができるような松の植生がみられます。
The outer moat’s earthenworks were completed in 1636. The following year, the Tokugawa shogunate order the group of eastern Japanese domainal lords previously mobilized to dig portions of the outer moat to plant a row of pine and cedar trees approximately 2.7 meters below the upper portion of those fortifications. The trees were to be planted 1.8 meters apart. In addition, they planted an inner row of smaller saplings parallel with the pine and cedar trees. This project was carried out under the direction of the Governor of Landscaping (later the Governor of Construction) and the maintenance of the newly planted fauna was entrusted to the warrior houses occupying estates along the outer moat and embankment between Ushigome-bashi Bridge and Kuichigai Gate. During the late-Edo period, the area was visited by Prussian diplomat Count Friedrich Albrecht zu Eulenburg. In his Record of the Eulenburg Expedition to Japan, he wrote, “Thick rows of fir trees and other conifers line the flat section crowning the castle walls and the walls’ interior section, and thousands of wild ducks inhabit the moats surface.” The rows of pine trees lining the embankment alongside Sanada-bori Moat (present-day Jōchi University Field) provide visitors with a sense of what the outer moat area was like in the Edo period.
Remnants of the stone walls that surrounded Ushigome-mon Gate can be found in their original form on the left and right sides of the Gate. Accordingly, they are important artifacts, which enable visitors to experience the scale and atmosphere of the stone walls that surrounded Edo Castle. During a 2013 archaeological survey, the stone wall on the northern side, which is visible here, was restored using original techniques and materials. The stone walls were constructed using a layering method in which stones on both ends were cut and chiseled in straight lines, and then laid in courses so that each stone fit tightly with the others. This was supported by a coursed masonry technique in which side joints passed through most sections of the wall. These methods gave the stone walls a precise, orderly appearance. In contrast, the stone walls’ lower portions and those touching the embankment were constructed using a comparatively imprecise layering technique in which small stones were pounded into gaps between the larger stones. The walls were constructed primarily using andesite from the Izu Peninsula. In addition, large granite stones transported from the Seto Inland Sea were used as cornerstones. Layering Techniques Used to Construct the Stone Walls The wall’s western side (Side B), which faced the outer moat, was constructed using a cutting-and-insertion method in which stones of different sizes were carefully chiseled to ensure that they fit tightly together. In contrast, the lower tier, which was buried under the embankment, was constructed using a comparatively rough pounding technique in which stones of different sizes and shapes were broken and beaten into the wall’s face. Continuing along the embankment, the protruding portion of the wall’s northern face (Side A) was constructed using the aforementioned cutting-and-insertion technique, whereas the section touching the embankment using the pounding technique. As a consequence, the northern face presents a less orderly appearance. In contrast, the wall’s south face (Side C), which was located inside the square enclosure surrounding the Gate, was comprised of square and rectangular stones and precisely constructed using the cutting-and-insertion technique. The stones used to construct the south face were carefully layered to ensure that side joints crossed the entire face of the wall. It is likely that this portion of the wall was so carefully constructed because it was located inside the enclosure and a space that those passing through would inevitably see. The Wall’s Internal Structure An examination of the wall’s internal structure reveals that cobblestones approximately the size of a fist, such as river stones and angular rocks, were embedded into it as backfill material. In the portion facing the road (Side C), each layer of the wall was embedded with a separate layer of backfill. The innermost layer (Layer IV) was precisely constructed using a technique in which flat stones were lined on their back. In contrast, the wall’s lower portion (Layer III) is filled with large cobble-stones, while the upper portion (Layer Il) is embedded with gemstone-shaped cobblestones the size of a fist and the outermost layer (Layer 1) is comprised of top soil. The existence of these distinct layers indicates that the rock walls have been repaired and refurbished several times in their history.
Also known as the Ushigome Gateway, Ushigome-mon Gate was constructed in 1636 under the direction of Hasuchika Tadateru, the lord of Tokushima domain. As described in the Illustrated Maps of Edo Castle’s Outer Gates, Ushigome-mon Gate’s inner section was surrounded by stone walls, which were arranged in a square shape to form an enclosure. It was comprised of two gates: a Korean-style outer gate, which led to a square courtyard and could be entered from the earthen bridge, and a large, two-story inner gate containing a timber-framed gatehouse. Even if enemy forces successfully penetrated the outer gate and entered the courtyard, they were prevented from entering the castle grounds by the large internal gate. Ushigome-mon Gate’s design enabled forces defending the Castle to attack the enemy from the walkway in the gatehouse’s upper tier and positions atop the stone walls surrounding the courtyard. In 1872, the Ministry of the Army assumed control of Edo Castle and were tasked with protecting the Imperial Palace. After taking control, they announced that many of the existing gates would be torn down in the name of security. Ultimately, they order the removal of 21 of the outer gates. The Ministry of the Army then assumed responsibility for guarding and maintaining the gates that remained in place. In an effort to develop Tokyo’s urban infrastructure, the Tokyo prefectural government moved carried out the actual work of removing the castle gates, elevated walkways above the gates, stone walls that surrounded many of the gates, and the earthen fortifications in their vicinity. In 1902, after the elevated walkway above Ushigome-mon Gate had been removed a portion of the stone walls surrounding its inner sections were torn down. However, the eastern and western walls were left in place and remain in existence today. The original form of the square courtyard that surrounded the gate is indicated by the surface of the road constructed in its place. It enables visitors to grasp the layout of the square courtyard that surrounded the Gate’s inner portion. The exhibit on the first floor provides a detailed description of the stone walls’ struc-ture. A cornerstone retrieved from the side of one Ushigome-mon Gate’s stone wallsis emblazoned with two seals: those of Hachisuka lemasa and Hachisuka Tadahide, who supervised. the construction of Ushigome-mon Gate’s walled courtyard.
神楽坂（新宿区）側に残る橋台 The Remained Bridge Stage Beside Kagurazaka 1989（平成元）年の地下鉄南北線工事における発掘調査で、牛込橋の新宿区側の橋詰に高さ9.5mの牛込見附の土橋の石垣が確認されました。石垣は軟弱な地盤の下位にある強固な砂層地盤を支持層として梯子胴木を敷いた上に築かれており、弱い地盤施工する際の工夫が伺えます。その他、当時の土橋の側溝の構造がわかる遺構なども発見されています。
An archaeological excavation carried out in 1989 in conjunction with the construction of Tokyo’s Nanboku Subway Line uncovered a 9.5-meter-high stone wall from the Shinjuku Ward-side approach to Ushigome-mon Gate’s earthen bridge. The stone wall was constructed on top of a crib base, which served as a support layer for the hardened stratum of sand comprising the bottom tier of the site’s weak foundation. This discovery provides us with insight into the techniques used during the Edo period when building on sites with an unstable foundation.
牛込門・牛込駅周辺の変遷 The Transition of Usigome-mon Gate and Ushigome Station Areas 外堀は、1660（万治３）年、牛込・和泉橋間の堀さらいが行われ、外堀（神田川）をさかのぼって、牛込橋までの通船が可能となり、神田川沿いに河岸ができました。牛込橋東側の堀端には、揚場町の「町方揚場」と御三家のひとつである「尾張様物揚場」があり、山の手の武家地や町人地へ薪や炭などの荷物を運ぶ軽子が、「軽子坂」を往来したといわれています。 牛込門から城内に入ると武家屋敷が連なり、他方、堀端から現在の神楽坂の辺りは、善国寺（毘沙門天）の坂下の地域が武家地、早稲田側には寺町が形成されました。寺の門前には町屋が建ち並び、江戸名所の一つとして賑わいを見せていました。 明治になると、城外の新宿区側には、空き家と化した武家屋敷跡が芸妓置屋や料亭となり、神楽坂花街が形成されていきました。他方、城内の千代田区側の武家屋敷跡に学校などが建てられました。 牛込土橋東側の堀は、1984（昭和59）年、再開発事業により暗渠となり、現在に至っています。また、鉄道整備においても削られずに残された牛込門周辺の土塁は、1911（明治44）年、牛込・喰違間の土手遊歩道を外堀保存のため公園とする計画が決定され、1927（昭和２）年、「東京市立土手公園」として開設されました。現在でも国史跡指定区域に、外濠公園として歴史的風致が保全されています。
In 1660, the section of the outer moat located between Ushigome-bashi and Izumi Bridges was dredged. This made it possible for boats to travel up the outer moat (Kanda River) to Ushigome-bashi Bridge. In addition, banks were constructed on both sides of the Kanda River. The bankside area on the eastern side of Ushigome-mon Bridge was home to the Agebachō neighborhood’s “community landing,” and “the Owari House Landing,” which was controlled by the Owari, one of the three branches of the Tokugawa clan. Both sites were used to offload arriving cargo. Porters transporting firewood and charcoal to warrior estates and commoner neighborhoods in the Edo’s Yamanote area are said to have traveled from these moat-side landings up an incline known as Hill of Karuko. Entering the castle grounds from Ushigome-mon Gate, warrior estates lined the street. The area located at the foot of Zenkoku Temple between the moat banks and present-day Kagurazaka was home to warrior estates and, on the Waseda side, there were Buddhist temples. Commoner residences lined the space in front of the temple gates and the area emerged as one of Edo’s most bustling sites. Entering the Meiji period, unoccupied former warrior estates outside the castle walls on the Shinjuku Ward side came to host restaurants and establishments employing geisha entertainers and courtesans. This led to the establishment of the Kagurazaka pleasure quarter. In contrast, schools and other institutions were constructed on the grounds of abandoned warrior estates inside the castle wall on the Chiyoda Ward side. In 1984, the moat on the eastern side of Ushigome-bashi Bridge was enclosed in conjunction with a local reedevelopment project. It remains covered today. In addition, in 1911, the government presented a plan to transform the portions of the moat embankment in the vicinity of Ushigome-mon Gate that survived the construction of the railroads into a public park and preserve remaining portions of the outer moat between Ushigome and Kuichigai as a pedestrian walkway. This resulted in the creation of Tokyo Dote City Park, which was founded in 1927. Even today, historic landscapes located inside the area officially designated as a national heritage site have been preserved in the form of Sotobori Park.
In 1636, Iemitsu, the third Tokugawa shogun, commanded domanial lords from around the country to construct an outer moat around Edo Castle. The following year, two rows of pine saplings were planted on the grass-covered embankment lining the outer moat. The outer row was comprised of large saplings, which were planted 2.7 meters from the embankment edge at intervals of 1.8 meters. The inner row consisted of an alternating series of large and small saplings arranged in a similar pattern. These rows supported the embarkment and shielded the castle. The portion of the embankment extending east from Ushigomemon Gate can be divided into two sections: one located along the outer moat and the other located inside the Gate. Photographic evidence indicates that the section lining the outer moat was a gentle earthen bank. The section inside the Gate is depicted in Views of Edo as a grass-covered landscape dotted with pine trees. During the Meiji period (1868-1912), the construction of wider roads and rail lines reduced the size of the embankment.
Underground, however, portions of the outer moat’s embankment, which constructed during the Tokugawa period using the ancient rammed earth (hanchiku) method, remain intact. This display recreates the earthen bank and rows of pines， which were located to the east Ushigomemon Gate’s box-shaped stone walls.
The section of the outer moat located between Ushigome to Ichigaya was constructed by utilizing the topography of the Kanda River valley. In addition, because the Yotsuya and Kojimachi sections of the moat were located on a ridgeline, which cut across the Kanda Plateau, moat construction in those areas required the execution of a large-scale infrastructure project in which sections of the Plateau were removed and the moat was extended to the valley in the vicinity of the reservoir on the Akasaka side. Groups of domainal lords were mobilized to carry out the project and each group was required to remove a predetermined amount of earth from the plateau. The outer moat reached its highest point in the vicinity of Kuichigai Gate. From there, the water level gradually lowered as it passed through the channels linking Sanada-bori Moat with the Kanda River. In order to control the flow of water and prevent flooding, weirs were constructed to around gates, such as Ushigome-mon Gate, which were located on earthen bridges. These weirs were then utilized to control the water level in the moat. Furthermore, utilizing the natural topography, large earthen fortifications were constructed by building up sections of the Kanda Plateau on the present-day Chiyoda Ward side of the moat in order to improve the Castle’s defenses. That project resulted in the establishment of a steep embankment. Edo Castle’s outer moat boasts a total length of approximately 14 kilometers. The approximately 4-kilometer, 38-hectare section between Ushigome and Akasaka Gates is a designated as a National Historic Site. Visitors to the site can see the ingeniously constructed outer moat filled with water, the stone walls of the Castle’s outer gates, and the shape of its earthen fortifications.
江戸城外堀 The History of Edo Castle Outer Moat 江戸城は、本丸・二の丸・三の丸・西の丸・北の丸・吹上からなる内郭を内堀が囲み、その表門が大手門でした。外堀は、雉子橋門から時計回りに、一橋門、神田橋門、常盤橋門など諸門をめぐり、呉服橋門から虎ノ門、溜池から四谷門、市谷門、牛込門を経て、現在の神田川に入り、小石川門から浅草門で、隅田川に至る堀でした。外堀工事は、1606（慶長11）年に雉子橋から溜池までの堀を構築後、1618（元和４）年に駿河台が掘削されて平川（現日本橋川）の流路に付け替えられ、神田川が誕生しました。この工事で、平川は堀留橋で締め切られ、独立した堀となりました。 1636（寛永13）年には、天下普請で外堀が構築され、江戸の総構が完成します。この工事は、雉子橋から虎ノ門に至る外堀の総石垣化と枡形築造を前田・細川・池田・黒田家など西国外様大名（石垣方六組）、牛込土橋から赤坂土橋にかけての外堀掘削と土塁の構築を東国大名（堀方七組）が行いました。 その後も幕府は、外堀を維持するために大名の手伝普請による堀さらいをしました。牛込～市谷間の堀は、市谷～四谷間より水位が下がり、土砂が堆積し、蓮が繁ったため、普請奉行の管理下で頻繁にさらいが行われました。また、町人にも堀にゴミを捨てないよう町触も出され、外堀の維持・管理が行われました。
Edo Castle’s inner hull was comprised of six citadels: the main, second, third, western, northern, and fukiage citadels. The entire inner hull was encircled by an internal moat and Ōte-mon Gate served as its main entrance. The Castle’s outer moat originated at Kijibashi-mon Gate and passed, in clockwise direction, through Hitotsubashi-mon, Kandabashi-mon, Tokiwa-bashi-mon, Gofukubashi-mon, and Torano-mon Gates. It then extended from Castle reservoir through Yotsuya-mon, Ichigaya-mon, and Ushigome-mon Gates before ultimately flowing into the present-day Kanda River. From there. it served as a canal, which passed through Koishikawa-mon and Asakusa-mon Gates and ultimately converged with the Sumida River. The outer moat’s development began in 1606 with the construction of a canal from Kiji-bashi Bridge to the Castle reservoir. The second stage in its evolution came in 1618, when portions of the Kanda Plateau were removed and the canal was redirected towards the Hira River. That process gave birth to the Kanda River and transformed the Hira River, which was closed off at Horidome-bashi Bridge, into an independent canal. The outer moat was finally completed in 1636, when feudal lords from eastern and western Japan were mobilized to construct its remaining portions. Specifically, western domainal lords, including the Maeda, Hosokawa, Ikeda, and Kuroda Houses, were ordered to supervise the construction of stone walls and the square masugata enclosures used to protect the castle gates along the section of outer moat between Kiji-bashi Bridge and Torano-mon Gate. In constrast, domainal lords from eastern Japan were order to dig a canal between Ushigome-bashi and Akasaka-bashi Bridges and construct earthen fortifications. In order to maintain the outer moat, the Tokugawa shogunate mobilized domainal lords from around the country to dredge it. In particular, the section of the moat between Ushigome and Ichigaya required frequent dredging because the water level often receded, resulting in the accumulation of silt on the moat floor and the development of water lilies on its surface. Such dredging projects were carried out under the supervision of the shogunate’s Governor of Construction. In addition, the city authori-ties attempted to keep the outer moat free of debris by issuing official proclamations banning the residents of commoner neigh-borhoods from disposing of garbage in the moat.
赤坂門：長崎大学附属図書館蔵
Akasaka-mon Gate: “Photo Tokyo Past and Present” Hiroshi Nozawa
喰違：『絵本江戸土産』国立国会図書館蔵
Kuichigai-mon Gate: “Edo Souvenir in Pictures” National Diet Library
そのほか：『旧江戸城写真帖』東京国立博物館蔵
Others: “Old Edo Castle Photo Collection” Tokyo National Museum
江戸城 The History of Edo Castle 江戸城は、平安時代末の江戸氏居館、室町時代の太田道灌、戦国時代の小田原北条氏の支城として受け継がれました。豊臣秀吉は、北条氏を滅ぼすと、徳川家康を関東に移封しました。1590（天正18）年、徳川家康は江戸城に入城し、江戸城と城下町の建設を始めました。家康入城時の江戸城には石垣はなく土塁のみで、日比谷も入り江で日本橋・京橋辺りも海面と同じ高さの湿地でした。 家康は、まず城内の寺を出し本丸を拡張し、城下町の武家地、町人地を整えました。次に、本丸の南の台地を削り西の丸を造成し、その残土で日比谷入り江を埋め立てました。1603（慶長８）年、幕府を開き実権を握った家康は、天下普請として、城と城下町建設に諸大名を動員しました。同じ年に、神田山を崩して日本橋南の地域を埋め立て、市街地の造成と日本橋の架橋を行い、翌年には日本橋を起点とする五街道を整備しました。1606（慶長11）年には二の丸・三の丸と城郭の整備、石垣築造を進め、翌年には天守が完成しました。なお、天守は1657（明暦３）年に大火で焼失した後、再建されませんでした。 1868（明治元）年、明治天皇が江戸城に入り皇居となり、1960（昭和35）年、江戸城内郭の堀が「江戸城跡」として国の特別史跡に指定されました。このほか、「江戸城外堀跡」と「常盤橋門跡」が史跡に、外桜田門、田安門、清水門とそれぞれの櫓門が重要文化財に指定されています。
Edo Castle’s origins can be traced to the establishment of the Edo Clan’s estate in the late-Heian period. During the Muromachi period, it served as the location of Ōta Dōkan’s branch castle. Entering the Warring States Period, it was controlled by the Hōjō Clan’s and served as the site of their branch castle. When Toyotomi Hideyoshi eradicated the Hōjō Clan in the late-sixteenth century, Tokugawa Ieyasu was sent to their former territory in the Kantō region. In 1590, leyasu assumed control of Edo Castle and initiated the Castle’s reconstruction and construction of the surrounding castle town. At the time, there were no stone walls on the Castle site. The only remaining features of the Hōjō Clan’s branch castle were its earthen fortifications. In addition, the Hibiya area was an inlet and the Nihonbashi and Kyōbashi areas were low-lying wetlands. leyasu began the reconstruction effort by removing temples from the site, expanding the Castle’s inner citadel, and supervising the construction of the city’s commoner districts and warrior estates. He then removed portions of the plateau immediately south of the inner citadel and constructed the western citadel. In addition, the inlet in Hibiya was filled in using the earth removed from the plateau. In 1603, leyasu, who had by then seized national political authority and established a tent government, mobilized domainal lords from the across the country to construct the remaining portions of Edo Castle and the surrounding city area. The same year, Kanda Hill was leveled and earth removed from the Hill was used to fill in the southern portions of the Nihonbashi area. The area was then developed and Nihon-bashi Bridge was constructed. The following year, an archipelago-wide network of five overland circuits originating from Nihon-bashi Bridge was established. In 1606, the second and third citadels and castle tower were constructed and work continued on the stone walls surrounding the Castle. By the following year, the Castle’s main keep was complete. In 1657, however, the Castle was destroyed by a fire and had to be reconstructed. In 1868, the Meiji emperor moved to Edo Castle and it came to serve as the imperial palace. In 1960, Edo Castle’s inner moat was classified as Edo Castle’s official ruins and designated a National Heritage Site. In addition, remaining portions of the Castle’s outer moat and the ruins of Tokiwabashi Gate received designation as Historical Landmarks. Lastly, the box-shaped, two-story gatehouses at Sakurada-mon, Tayasu-mon, and Shimizu-mon Gates were designated as Important National Treasures.
