The Kintaikyo Bridge is a historical wooden arch bridge, in the city of Iwakuni, in Yamaguchi Prefecture, Japan.
The bridge was built in 1673, spanning the beautiful Nishiki River in a series of five wooden arches, and the bridge is located on the foot of Mt.Yokoyama, at the top of which lies Iwakuni Castle.
Declared a National Treasure in 1922, Kikkou Park, which includes the bridge and castle, is one of the most popular tourist destinations in Japan, especially for the Cherry Blossom festival in the spring and the autumn color change of the Japanese Maples.
After Iwakuni Castle was built in 1601 by Kikkawa Hiroie, the first lord of Iwakuni Domain, a series of wooden bridges were built, all of which were destroyed by floods several times before the construction of the iconic Kintai Bridge. It was built in 1673 by the third lord, Kikkawa Hiroyoshi, new stone piers replaced the old wooden ones and it was thought to be flood-proof; however, the bridge was still destroyed by a flood the next year. As a result, they redesigned the stone piers for greater strength, and a special tax was created to maintain the bridge. This maintenance consisted of being rebuilt periodically: every 20 years for 3 spans in the middle, every 40 years for 2 spans connecting to the riverside. In this way, the bridge was not destroyed by floods again until 1950 by flooding from typhoon "Kezia." It had been in a weakened state at the time, both because the Japanese had stopped maintaining the bridge during World War II and the year before the typhoon, to expand the US Marine Corps Air Station in Iwakuni, a large amount of gravel was taken by the US Military Force from the river around the bridge, strengthening the flow of the river. In 1953, the bridge was once again reconstructed using very similar techniques to the original; however, they used metal nails (made from the same tatara iron as the Katana) to increase its durability. This 1953 reconstruction, partially restored in 2001 and 2004, still stands today.
The bridge is composed by five sequential wooden arch bridges on four stone built piers as well as two of wooden piers on the dry riverbed where the bridge begins and ends. Each of the three middle spans is 35.1 meters long, while the two end spans are 34.8 meters for a total length of about 175 meters with a width of 5 meters.
For nearly three hundred years the many versions of the bridge stood without the use of metal nails. They achieved this by careful fitting of the wooden parts and by building up thick girders by clamping and binding them together with metal belts. The main wooden parts of the bridge would then be covered by sheets of copper. The shape and weight of the bridge made it extremely strong from the top, but incredibly weak from underneath, flood water rushing along the river would simply lift the bridge up and wash it downstream. So the bridge was designed so that the wooden pathway merely "floats" on top of the frame of the bridge by using mortise and tenon joints. This would allow rising flood waters to simply lift out the pathway and carry it off down stream while sparing the main structure.