1. Could a stone wall stand in the sea where filled earth washed away?
It was decided in 1869 to run a railway between Tokyo and Yokohama. However, there is a theory that the area around Takanawa was not handed over to the railway side because the Ministry of Military Affairs deemed it necessary for national defense. Instead, about 2.7 km (1.7 miles) from Shiba to Shinagawa Station was built on the sea. The materials note that this is "according to one theory" [1].
The construction was guided by British engineer Edmund Morel and handled by the Railway Bureau of the Ministry of Civil Affairs (later the Railway Bureau of the Ministry of Public Works). Work did not go as planned because the earth and sand they filled in were washed away by waves, causing the embankment to collapse. It was completed in September 1872. Construction began around 1870, taking about 2 years [1][4].
In work on the sea, it is likely that the structure under and behind the stone wall shared the job, not just the wall itself. What was placed under the stone wall?
2. The wooden "dougii" base and the piles driven on the sea side of the wall
The excavated sea-side stone wall has been confirmed to have up to 15 layers. The base at the very bottom is made of squared timber called "dougii," which supports the "neishi" (root stones) of the lowest layer. Above this, stones are stacked horizontally one layer at a time at an angle of about 30 degrees [2].
On the sea side of the dougii, piles have been found in rows. Kei Aoki, who was involved in the investigation (Kokugakuin University), explains that many piles were driven on the sea side outside the embankment to prevent it from collapsing due to seawater erosion. He identifies this as a technique developed at the Shinagawa batteries in the late Edo period [4].
The wooden base and piles seem to have had the role of supporting the stone wall from below and outside so it would not sink or wash away. However, sea embankments worry about more than just wave power. What happens to the water that accumulates behind the stone wall?
3. How the small stones behind the wall helped drain water
Small stones called "uragomeishi" are packed behind the stone wall [1]. Aoki states that a thick layer of stones for drainage behind the wall and the gentle slope of the embankment are major features of the structure. He notes that neither of these features is seen in the Shinagawa batteries [4].
Aoki explains why drainage is needed. River embankments aim to prevent overflow during floods, but coastal embankments have seawater seeping in constantly. Therefore, they need a drainage plan, and their structure differs significantly from river embankments. The sea-side slope of the embankment is around 30 degrees, which is gentler than the Shinagawa batteries [4].
The stone wall was not just a wall of stacked stones; it seems to have been a structure that included a layer to let water escape from behind. Inside this is the main body of the embankment, filled with earth. How was this earth put into the sea?
4. How earth was filled and piled up in the core of the embankment
The core of the embankment is assumed to have a structure where earth and sand were first filled in, then piled up, with stone walls stacked on both the sea and mountain sides [2]. Materials from a tour explain that the earth used in the core was "dotan," a very hard soil containing hard clay [1].
In a confirmation survey by Minato Ward in 2024, dougii, root stones, and 5 layers of stone wall were found under the sea-side wall from the opening period around 1872. The walls of the trench (test excavation) showed that filling was done from the sea side using sea sand, white clay, and loam soil. However, the report notes that the content may change with future surveys [3].
The embankment structure differs by location, and differences in the type of fill and stacking direction revealed spots thought to be boundaries between construction sections at the time [1]. The history of the construction remained in the earth. How was this interior investigated?
5. How the embankment, thought to be demolished, was found at Shinagawa Station in 2019
In April 2019, part of the stone wall was found during improvement work at Shinagawa Station. This was the clue that revealed the embankment, thought to have been demolished during surrounding reclamation, still remained. It appeared in relatively good condition under the tracks of the old Yamanote and old Keihin-Tohoku lines, with the ballast (stones laid on the track) from the opening period also remaining [2].
In the excavation, the embankment was cut vertically to observe the interior. Because it revealed how it was built, the procedures, materials used, and application of traditional techniques, Minato Ward positions this as "valuable information replacing a design blueprint" [1].
The mountain-side stone wall used a "tani-zumi" method, using stones at an angle. It is thought to be from when the embankment was widened for the third track in 1899 [2]. In September 2021, about 120 m (394 ft) of the embankment was added to the list of National Historic Sites [1]. The stone wall on the sea is now speaking from inside the earth. Where did this technology come from?
6. How battery building techniques and British ideas were combined in the embankment
Stone materials for the wall included stones from the batteries and the Takanawa coast [1]. It seems that not just materials but also techniques were inherited from the batteries. Aoki identifies the method of building the stone wall covering the slope and the many piles driven on the sea side as technology for marine structures developed at the Shinagawa batteries in the late Edo period [4].
On the other hand, the gentle slope of the embankment and the thick stone drainage behind the wall are not seen in the Shinagawa batteries. Aoki writes that he "considers" these to be of British origin, due to the presence of Edmund Morel, the first Chief Engineer of the Railway, and Katsu Inoue, who studied civil engineering and railway technology in Britain. However, he also states that because the structure is very different from river embankments, elements other than traditional technology must be considered [4].
The stone wall of the embankment seems to have been a project where the experience of the sea accumulated at the batteries and ideas considered to be of British origin met in one embankment. The mixing of these ideas appeared in the hidden parts, such as the wood under the wall and the small stones behind it.
7. How you can investigate stone walls yourself by comparing how stones are stacked
Compare how stones are stacked. Look for stone walls nearby and observe if the stones are aligned horizontally layer by layer or arranged at an angle. Even in the embankment, the stacking method differed between the wall from the opening period and the widened part from 1899. If there are small holes near the bottom of a wall, it might be a way to let water escape. Be careful of cars and your footing near roads and walls.
If you want to read materials, the Minato Ward Board of Education's materials on the "Takanawa Embankment" include terms like dougii and uragomeishi, along with excavation photos. Check the official Minato Ward information for current site visibility.