Mino Bridge

Japan's Oldest Surviving Modern Suspension Bridge

Minohashi Bridge (美濃橋, read Minohashi rather than Minobashi) crosses the Nagara River in Mino City, Gifu Prefecture, was completed in August 1916 during the Taisho era, and was designated an Important Cultural Property on 30 May 2003.

It is the oldest modern suspension bridge still standing in Japan. That claim rests on a specific definition: a bridge with main cables anchored at both banks, hangers carrying a deck, and a stiffening truss to control movement. Older suspension bridges exist in Japan as vine or rope crossings. None of them is engineered on these principles.

The bridge spans the Nagara at a point north of central Mino where the river curves west around Mount Ogura. It runs almost perpendicular to the current. The deck is 113 meters long and 3.1 meters wide, with a span between towers of 116 meters, in a single-span stiffened suspension design.

The project came from a petition. Mino town and Asono village on the opposite bank both wanted a crossing that would hold during high water, and Gifu Prefecture built it as a subsidized public work. Ground was broken in August 1915 and the bridge opened the following August.

Who Built It, and What Was Recorded

Toya Inazo, an engineer with Gifu Prefecture who had graduated in civil engineering from Imperial University in 1888, led the work. Contemporary newspapers name two others involved: Hori Usaburo, a prefectural technician who graduated from Nagoya Higher Technical School in 1909 and later took the name Hori Masayoshi, and Tamai Yoshio, an official of Mugi District.

The construction dates come from two separate documents rather than a single record. The starting month appears on the invitation issued for the opening ceremony; the completion month comes from the Osaka Asahi Shimbun of 18 August 1916. A maker's plate on the left-bank side of the stiffening truss reads that it was manufactured by Nagoya Ironworks and completed in July 1916.

The Agency for Cultural Affairs cited two grounds for designation: technical excellence, and high historical value. The bridge carries the full vocabulary of modern suspension engineering through its entire structural body, and its 116-meter span was among the longest built in Japan at the time.

After it opened, Minohashi served as one of the main road crossings of the Nagara. As other bridges went up, including the New Mino Bridge, traffic fell away. Since the 1965 to 1974 period it has been restricted to pedestrians.

Details Worth Stopping For

The towers stand 9.8 meters high, built of reinforced concrete. Each carries an iron sliding bearing at the top, allowing the main cable to shift slightly as loads change. The bases are faced in cobblestone with the corners laid in an interlocking pattern resembling stacked timbers. The underside of each tower's crossbeam is cut as an elliptical arch, and the bridge name is carved into the landward face: the right-bank tower reads minohashi in kana, the left-bank tower reads 美濃橋 in characters.

The main cables are built from nineteen wires in six strands around a core, hung at a sag ratio of one to fifteen. The hanger cables use thirty-seven wires in six strands, and each connects to a floor beam through a turnbuckle, the threaded fitting that allows tension to be adjusted after installation.

The two anchorages differ from one another, and the difference is worth knowing before you walk across. On the right bank, a concrete mass faced in cobblestone with a mortar-washed top sits about 43 meters northwest of the tower, with seven strand ropes embedded in it and connected to iron sockets for tension adjustment. On the left bank there is no such block. The main cable runs into a tunnel bored through the rock of Mount Ogura and is anchored inside, with the cavity filled with concrete.

The stiffening truss is a double Warren type, assembled from angle sections and T-bar riveted together. Every three panels, a diagonal ties the upper chord to a floor beam.

Apart from the wooden deck boards, replaced in 1983 and again in 1999, the members you see are the ones installed at construction. A five-year restoration beginning in 2016 followed detailed investigation and seismic assessment started in 2012. Where members had to be replaced, the work was done with rivets rather than high-tension bolts or welding, keeping the original technique in use.

The bridge reopened on 9 March 2021. Night lighting was installed during the restoration, and photographers now come after dark. Crossing is free and unrestricted by hour. Bicycles are permitted, cars are not, and a sign at each approach limits the bridge to twenty people at a time. The deck moves underfoot and the boards creak; visitors uneasy with movement should know this in advance.

The riverbank below draws swimmers and barbecue parties in summer. Jumping from the bridge has caused repeated drowning deaths, and Mino City and neighboring Seki City both warn against it. Mino Ota Station on the Nagaragawa Railway is the nearest rail access, and the preserved merchant district of Mino Udatsu, with its fire-wall roof ridges, lies a short distance south.