A 1912 Plate Girder Still in Its Original Dress
Where the Watarase Keikoku line crosses the Kawaguchi River in Kiryu, Gunma Prefecture, it rides over a short steel bridge that has changed remarkably little in more than a century. The Shirori Bridge spans twenty meters in a single length of girder, carrying one track over a tributary of the Watarase. It is a deck-type plate girder, meaning the track sits on top of the steelwork rather than running between the beams, so from a passing train the bridge is almost invisible underfoot.
The span measures sixty feet in the imperial units its builders used, a reminder that Japanese railway engineering of the 1910s still leaned on British practice. What sets this bridge apart to an engineer's eye is how much of the original detail survives. The vertical plates that stiffen the girder web are cut in a distinctive J shape. The box-form brackets that tie the main girders together carry no diagonal bracing, the reinforcement that was often added to older bridges as loads grew heavier. Here the brackets remain as they were first riveted, without that later stiffening, which makes the structure an unusually honest record of how such a bridge looked when new.
A Copper-Mine Railway, Registered as Heritage
The bridge went into service in 1912, when the private Ashio Railway pushed its line up the Watarase gorge to carry ore down from the Ashio copper mine. That mine was one of the largest in Asia and also the site of Japan's earliest major industrial pollution case, the Ashio copper poisoning that damaged farmland along the river. The railway was nationalized in 1918, ran as the government's Ashio Line for decades, and passed in 1989 to the third-sector Watarase Keikoku Railway after the mine had closed.
On 2 November 2009 the Shirori Bridge was entered as a Registered Tangible Cultural Property, with formal notice on 19 November, as part of a group of about three dozen structures along the line listed together. Japan's registration system, a lighter category than the "Important Cultural Property" designation, protects structures generally over fifty years old while letting them stay in use. The stated ground for listing is that the bridge contributes to the historic landscape of the country, a landscape shaped by early twentieth-century mine railways threading through steep river valleys.
Finding It Along the Line
The Shirori Bridge sits about forty meters southwest of the Shirori Tunnel, so bridge and tunnel form a pair that a rider passes within seconds of each other. This part of the route runs through the Kurohone district of Kiryu, quieter and more wooded than the towns downstream. Because the track is on top of the girders, the bridge reads best from the side, from a riverbank vantage or a road crossing where the plate girder and its box brackets show against the water.
The bridge is live railway infrastructure and cannot be walked. The rewarding way to encounter it is from a seat on the line, and the open-sided torokko sightseeing carriages that run in the warmer months make the river crossings especially vivid. Anyone drawn to early steel-bridge engineering will find the neighboring tunnels and the string of 1912 structures nearby worth tracing along the gorge.
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Q&A
- What kind of bridge is it?
- A single-track deck-type steel plate girder, twenty meters long, spanning the Kawaguchi River. The track runs on top of the girders.
- What makes it notable among old railway bridges?
- It keeps its original form, including J-shaped web stiffeners and box brackets that were never fitted with the diagonal bracing often added to bridges later.
- How do I see it?
- From a train on the Watarase Keikoku line, or from the riverbank nearby. It is active railway and cannot be crossed on foot.
- Is the Shirori Tunnel close by?
- Yes. The tunnel is about forty meters northeast of the bridge, so the two come in quick succession.
Basic Information
| Name | Watarase Keikoku Railway Shirori Bridge |
|---|---|
| Location | Shukumawari, Kurohone-cho, Kiryu City, Gunma Prefecture |
| Designation | Registered Tangible Cultural Property (registered 2 November 2009; notice 19 November 2009) |
| Registration No. | 10-0295 |
| Count | 1 structure |
| Date | 1912 |
| Structure | Steel single-girder bridge, span 20 m, with abutments |
| Access | Viewable from trains and the nearby riverbank; the bridge is not open to pedestrians |
References
- National Database of Designated Cultural Properties, Agency for Cultural Affairs — Watarase Keikoku Railway Shirori Bridge
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00007868
- 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