The Battle of Zhennan Pass was a significant battle of the Sino-French War which occurred on March 23, 1885 and was referred to at the time, in Western media, as the Battle of Bang Bo. The Franco-Chinese War lasted from September 1881 to 1885. ... March 23 is the 82nd day of the year in the Gregorian Calendar (83rd in Leap years). ... 1885 is a common year starting on Thursday. ...

Isolated at the citadel of Lang Son in northern Tonkin, a French brigade attempted to relieve pressure by Chinese forces by attacking Bang Bo, a fortified camp across the border in Guangxi province. The French faced approximately 10,000 Chinese soldiers from the "Army of the Two Guangs" with less than a thousand rifles. Lang Son, a city in far northern Vietnam, is the capital of Lang Son province. ... Tonkin, also spelled Tongkin or Tongking, is the northernmost part of Vietnam, south of Chinas Yunnan and Guangxi Provinces, east of northern Laos, and west of the Gulf of Tonkin. ... Guangxi (Zhuang: Gvangjsih; old orthography: ; Simplified Chinese: 广西; Traditional Chinese: 廣西; pinyin: ; Wade-Giles: Kuang-hsi; Postal System Pinyin: Kwangsi), full name Guangxi Zhuang Autonomous Region (Zhuang: Gvangjsih Bouxcuengh Swcigih; old orthography: ; Simplified Chinese: 广西壮族自治区; Traditional Chinese: 廣西壯族自治區; pinyin: ) is a Zhuang autonomous region of the Peoples Republic of China. ...

After a two-day battle, the French effort failed in the face of logistical shortages, miscommunications, and numerical handicaps. The brigade retreated back in Tonkin, leading to a Chinese counterattack at Ky Lua (which was defeated) and the controversial retreat from Lang Son. Lang Son, a city in far northern Vietnam, is the capital of Lang Son province. ...