Japan did both occupy Thailand and Burma during the War, however when the sea route through the Strait of Malacca became vulnerable an alternative way of transporting support to the troops in Burma was needed. A railway connection between Thailand and Burma was already surveyed at the beginning of the 20th century by the British, but was considered too difficult to be built. The Japanese nevertheless started the project in June 1942, connecting Kanchanaburi with Thanbyuzayat by the Three Pagoda Pass. Construction started simultaneously at the Thai and the Burmese side.
After 17 months the 415 kilometers of railway were finished, when on October 17, 1943 the two lines met about 18 km south of the Three Pagoda Pass at Konkuita. While most of the POW were then transferred to Japan, those left for maintenance still suffered from the bad living conditions as well as allied air raids.
The most famous part of the railway is the bridge over the river Kwae Yai, however named River Kwai in the book by Pierre Boulle and the later film The Bridge on the River Kwai. The first wooden bridge over the Kwae Noi was finished in February 1943, followed by a concrete and steel bridge in June 1943. Both bridges were destroyed on April 2, 1945, but had been damaged and repaired several times before already.
After the war the railway was in too bad a state to be used for the civil Thai railway system, and needed heavy reconstruction. It was also converted from 1 meter narrow gauge to standard gauge. In June 1949 the first part from Kanchanaburi to Nong Pladuk was finished, in April 1952 the next section up to Wampo, and finally in July 1957 up to Nam Tok, making about 50 kilometers of the death railway still in use. Since the 1990s there are plans to rebuild the complete railway, but these plans haven't gotten anywhere concrete yet.
The living and working conditions on the railway were horrific. About 25% of the POW workers died because of overworking, malnutrition and diseases like cholera, malaria and dysentery. The death rate of the asian workers was even higher, however the numbers for them are only estimates as the Japanese didn't bother to count them.
Several memorials were built on the Thai side after the war. Directly at the bridge is a memorial plaque, and a historic locomotive is on display as well. Another memorial built by the Australians is at the Hellfire Pass, a landcut which did cost most of lives of all the building. The main POW cemetery is about 1 kilometer north of the city Kanchanaburi. 6.982 POW were buried there, mostly British, Dutch, Australian and American. A smaller cemetery a bit further outside city is Chong Kai with 1.750 graves. Both are maintained by the Commonwealth Graves Commission.
An excellent museum dedicated to those who lost their lives constructing the railway called "The Thailand-Burma Railway Museum" was opened in Kanchanaburi in March 2003. Another older museum in Kanchanaburi is the JEATH War Museum.