The Trans-Mongolian Railway follows an ancient tea-caravan route from China to Russia and connects Ulan-Ude, on the Trans-Baikal (Trans-Siberian) railway in Russia, with the Chinese city of Jining, by way of Ulaanbaatar in Mongolia.
Other important stops are Sükhbaatar, Darkhan, Choir, and Zamyn-Üüd/Erenhot (border crossing and gauge-changing station). The line was built between 1949 and 1961. In most of Mongolia, it is single track, and in China double track. The gauge is 1,520 mm (4 ft 11 27⁄32 in) in Russia and Mongolia and 1,435 mm (4 ft 8 1⁄2 in) in China. There are important branches leading to Erdenet and Baganuur.
Railway development came late to Mongolia. Construction of the Trans-Mongolian line began in 1947, reaching Ulan Bator from the north in 1950 and the Chinese border in 1955. Before that the only railways in Mongolia had been a 43 km (27 mi) line (opened in 1938) connecting the coal mines at Nalaikh to the capital and a Soviet-built 236 km (147 mi) freight-only branch (completed in 1939) from Borzya on the Trans-Siberian Railway to Bayantümen, Dornod near Choibalsan in north-eastern Mongolia.