Old Taisho Forest Road Sagawa Bridge

Former Taisho Forest Road Sagawa Bridge: A Living Monument to Shimanto's Forestry Heritage

Deep in the mountainous heart of Shimanto Town, Kochi Prefecture, a graceful triple-arch bridge rises above the emerald waters of the Yusuhara River. Known locally as "Megane-bashi" (Spectacle Bridge) for the way its arches reflect on the surface of the Tsuga Dam reservoir to resemble a pair of eyeglasses, the Former Taisho Forest Road Sagawa Bridge (旧大正林道佐川橋) stands as one of the most evocative reminders of Japan's forestry heritage in the Shimanto River basin.

Completed around 1944, this reinforced concrete bridge was built to carry locomotive-hauled trolley cars loaded with timber from the national forests of Mount Sagawa to the lumber yards in the town of Tanono (present-day Shimanto Town Taisho). Today, draped in ivy and moss, the bridge presents a hauntingly beautiful scene that visitors often compare to the landscapes of Studio Ghibli films. It is a Registered Tangible Cultural Property of Japan and a designated Kochi Prefecture Modern Heritage site.

The History of the Taisho Forest Road

The story of the Sagawa Bridge is inseparable from the broader history of forestry along the Shimanto River, Japan's last remaining clear-flowing river. The Yusuhara River valley, where the bridge stands, has been a center of forestry since the Edo period, when the Tosa Domain designated vast tracts of mountain forest as "otomeyama" (protected reserves) to supply high-quality timber for construction and shipbuilding.

With the dawn of the modern era, the national government inherited these forests and began developing them on an industrial scale. In 1911, the Miura Timber Company laid the first forest railway in the Shimanto River system between Nakatsugawa and Onaro, pioneering mechanized timber transportation in the region. In 1925, the Forestry Bureau purchased this railway and extended it along the Yusuhara River, establishing lumber yards and sawmills in Tanono while pushing the track further into the mountain interior.

The Taisho Forest Road ultimately branched into two main lines: one following the Yusuhara River to Sakashima-yama in Shimotsui, and the other running along the Nakatsugawa River to Osuji-yama. When the line was extended from Sakashima to Mount Sagawa, the construction of a major bridge became necessary at the point where the Harai River flows into the Yusuhara River. This bridge was the Sagawa Bridge.

Why It Was Designated as a Cultural Property

The Former Taisho Forest Road Sagawa Bridge was registered as a Tangible Cultural Property on March 7, 2008. Its designation recognizes several layers of significance.

Architecturally, the bridge is a remarkable feat of wartime-era civil engineering. Standing 20 meters high with a total length of 82 meters and a width of 2 meters, it features three segmental arches — a central span of 30 meters flanked by two arches of 20 meters each. Stone retaining walls of "tani-zumi" (valley masonry) construction extend continuously along both riverbanks, demonstrating the high level of craftsmanship available even during the difficult final years of World War II.

Historically, the bridge represents the largest structure on the former Taisho Forest Road and serves as a powerful symbol of the national forest enterprise that drove economic development across the Shimanto River basin from the Meiji era through the Showa era. The current bridge replaced an earlier structure that was submerged following the construction of the Tsuga Dam, making it a testament to the evolving relationship between forestry infrastructure and hydroelectric development.

The bridge is also an integral component of the "Cultural Landscape of the Shimanto River Basin (Taisho Oku-Shimanto Area)," a nationally selected Important Cultural Landscape that tells the comprehensive story of how communities in this region lived with and shaped their natural environment through forestry, agriculture, and river transportation.

Highlights and Things to See

Surrounding Area

The Shimotsui district, where the Sagawa Bridge is located, is a tranquil mountain village surrounded by forests along the shores of the Tsuga Dam reservoir. Despite its remote setting, the area offers several worthwhile attractions for visitors.

Shimotsui Onsen is a small, town-operated hot spring inn located nearby, offering day-use bathing in hydrogen sulfide spring water — a perfect way to relax after exploring the bridge and walking trails. The Shimanto River itself, renowned as Japan's last clear-flowing river, provides opportunities for canoeing, rafting, and swimming at various points downstream. The Shimanto River basin is also famous for its submersible bridges (chinka-bashi), unique low-profile bridges designed to go underwater during floods rather than resist them.

For those traveling between the Shimanto area and Yusuhara Town or the Shikoku Karst plateau, the scenic drive along National Route 439 passes directly through the Shimotsui district, making the Sagawa Bridge a natural stopping point. The road, sometimes called "Japan's most challenging national route" for its narrow, winding mountain passages, offers spectacular scenery throughout.