A Straight Brick Tunnel Built to Japan's First Standard
The Shirori Tunnel runs straight for eighty-two meters through rock in the Kurohone district of Kiryu, Gunma Prefecture, carrying a single track of the Watarase Keikoku line. Unlike some of the curving bores further up the gorge, this one is a clean straight line, so the far portal shows as a small bright arch the moment a train enters. The cross-section is a horseshoe, and the lining is brick laid four courses deep, the standard heavy section used where a mountainside presses in on the track.
What gives the tunnel its historical weight is the shape of that cross-section. It follows, almost exactly, the profile of the government railways' "Tessaku-otsu No. 4375" pattern, the first standardized tunnel specification drawn up in Japan. Before such standards, each tunnel was worked out on its own terms. The Shirori Tunnel is an early example of the country adopting a repeatable engineering template for railway building. The south portal is finished in coursed brickwork close to what Japanese builders call French bond, alternating the long and short faces of the bricks within each row so the wall reads as a tight, regular pattern.
From Ore Line to Registered Heritage
The tunnel opened in 1912 as the private Ashio Railway carried its line up the Watarase valley to reach the Ashio copper mine. The mine was among the largest in Asia and also the source of the Ashio copper poisoning, an early industrial pollution disaster that harmed the river's farmland. The line was nationalized in 1918, served for decades as the government's Ashio Line, and was taken over by the third-sector Watarase Keikoku Railway in 1989, sixteen years after the mine closed.
On 2 November 2009, with formal notice on 19 November, the Shirori Tunnel became a Registered Tangible Cultural Property, one of about three dozen structures along the line listed as a group. Registration is a lighter form of heritage protection than the "Important Cultural Property" designation, covering structures generally more than fifty years old and allowing continued use. The listing rests on the tunnel's contribution to the historic landscape of the country, the landscape of a mountain mine railway that still runs.
Where to Look, and a Note on the Name
The Shirori Tunnel and the Shirori Bridge share a name and sit close together, the bridge about forty meters to the southwest across the Kawaguchi River. Both belong to the same short, wooded stretch through Kurohone. The tunnel lies roughly 1,800 meters southwest of the Edogawa Bridge, another 1912 structure on the line, so a rider tracing the gorge passes a sequence of contemporaries in a few minutes of travel.
Because it carries live track, the tunnel cannot be walked or entered. The way to see it is from a train, and the brick portal is best appreciated as the carriage slows on approach. The open-sided torokko sightseeing trains that run in the warmer months give the fullest sense of the tunnels and bridges along this part of the line. For visitors interested in early Japanese railway engineering, the pairing of the straight Shirori Tunnel here with the gently curving Godo tunnels upstream shows two solutions to the same problem of threading a valley.
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Q&A
- What is special about this tunnel's design?
- Its cross-section closely follows the "Tessaku-otsu No. 4375" pattern, the first standardized tunnel specification in Japan, making it an early example of standardized railway engineering.
- Is this the same as the Shirori Bridge?
- No. They share a name and stand close together, but one is a tunnel and the other a steel bridge over the Kawaguchi River, about forty meters apart. Both date to 1912.
- How is the brickwork laid?
- The lining is four courses deep in a horseshoe section, and the south portal uses coursed brickwork close to French bond, alternating headers and stretchers.
- Can I visit the tunnel itself?
- No. It is active railway and closed to pedestrians. You can see it from a train on the Watarase Keikoku line.
Basic Information
| Name | Watarase Keikoku Railway Shirori Tunnel |
|---|---|
| Location | Shukumawari, Kurohone-cho, Kiryu City, Gunma Prefecture |
| Designation | Registered Tangible Cultural Property (registered 2 November 2009; notice 19 November 2009) |
| Registration No. | 10-0294 |
| Count | 1 structure |
| Date | 1912 |
| Structure | Brick and stone construction, 82 m long, with retaining wall |
| Access | Viewable from trains on the Watarase Keikoku line; the tunnel is not open to the public |
References
- National Database of Designated Cultural Properties, Agency for Cultural Affairs — Watarase Keikoku Railway Shirori Tunnel
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00007867
- Watarase Keikoku Railway Co., Ltd. — Company History
- https://www.watetsu.com/company/history.php
- Watarase Keikoku Line (Japanese Wikipedia)
- https://ja.wikipedia.org/wiki/わたらせ渓谷鐵道わたらせ渓谷線
Last verified: 2026.07.02