The bridge over the Mae Klong (or Kwai Yai, or whatever) really was part of the death railway, built with prisoner and slave labor by the Japanese during World War II. There were actually two bridges built over the river here. A wooden bridge like you see built in the movie (which was actually shot in Sri Lanka) was built first about 100 meters up-river from the current bridge to expedite construction on the line beyond the river. The concrete and steel "main" bridge was added during the war when the steel became available.
Both bridges were bombed by allied planes near the end of the war. The squarish center spans of the bridge are post-war replacements. The wooden bridge was demolished after the war since its thick structure blocked the flow of the river.
The Death Railway was built during World War II by the labor of the war prisoner and the Asian labor forced by the Japanese troop. During that time, Thailand was the alliance of Japan and also gave a big support to the Japanese army. The Death Railway was a route to pass Myanmar and to invade India. Japan was aware that by using the sea troop to fight with England, their armies would be attacked by the alliances. From this reason, they decided to build this railway. The railway was named after the event in the history. There is a saying that the numbers of the railway is equal to the numbers of the death labor used to build this railway.
The Death Railway starts from Nong Pladuk station, Amphur Baanpong, Ratchaburi to Kanchanaburi crossing the Kwai Yai River to the west, passing Chedi Sam-Ong to the destination at Thanbyuzayat in Myanmar, which is 415 kilometers altogether with 37 stops. This railway was completed on 25th October 1943. During the building period, there were many labors who sacrificed their lives with sickness and by the torturing of the Japanese army. The bridge here was named River Kwai Bridge. This construction built a big motivation for the Japanese armies and also a big scar in the labors’ heart. The history was still unforgettable among the people’s heart.
Nowadays, the Death Railway was opened for the tourists to visit. However, there are some parts that were deserted since Japan lost the war. The State Railway of Thailand has offered the Thonburi-Namtok line for the tourists who wish to visit this place and a special line Bangkok-Namtok on the weekends and holidays. The most popular point is the River Kwai Bridge and the Krasae Cave, which is a curve bridge that follows the bank of Kwai Noi River. The train stops at Krasae Cave at 1:30 p.m. The tourists can travel in advance in order to be on time to see the picture of the train arriving at this station.