Lạng Sơn
Lạng Sơn () is a city in far northern Vietnam, which is the capital of Lạng Sơn Province. It is accessible by road and rail from Hanoi, the Vietnamese capital, and it is the northernmost point on National Route 1. History. Due to its geography as Vietnam's gateway to China, Lạng Sơn and its ancient citadel have been in the path of many invasions, and were the site of three French defeats during the colonial era. Occupied by Qing forces during the military buildup that preceded the Sino-French War, the city was occupied by France after the  two-week Lạng Sơn Campaign in February 1885. However, the brigade there conducted a hasty retreat after a failed attack at the Battle of Bang Bo into China; the "retreat from Lạng Sơn" became the most controversial aspect of the war and led to the fall of Jules Ferry's ministry. Outnumbered French colonial forces clashed with the Japanese 5th Division in the Battle of Lạng Sơn during the Japanese Vietnam Expedition on 22 September 1940. The French were again compelled to retreat hastily. In 1945 it was again the scene of heavy fighting during the Japanese coup d'état in  French Indochina. After the end of the Pacific War, the French colonial army established a permanent garrison there, which served as the logistics hub for the French border fortresses. It was evacuated in 1950 during Võ Nguyên Giáp's offensive against the French border forts, considered a turning point in the Indochina War. The city was the center of fighting during the Sino-Vietnamese War of 1979, and sustained extensive damage. Geology and climate. The surface rocks in the area are a Permian limestone, overlain by the early Triassic Lang Son Formation, consisting of flyschoid beds with interbedded sandstones, siltstones  and clay shales and some felsic volcanics.