Zhangjiakou or Changkiakow (both: jäng-jēä-kou) [key], Mongolian Kalgan, city (1994 est. pop. 615,300), NW Hebei prov., China, near a gateway of the Great Wall and on the Beijing-Russia RR. A major trade center for N China and Mongolia, it has food-processing plants, machine shops, and tanneries. The meeting place of caravans traveling from Beijing to Ulaanbaatar, it was an important military center under the Manchu dynasty but declined somewhat after the opening (1905) of the Trans-Siberian RR. In 1928 it became the capital of Chahar prov., which was abolished in 1952. The name sometimes appears as Chang-chia-k'ou.