The Banners (In Manchu: gūsa, In Chinese: 旗 qi2) were Manchu military and social organizations established by Nurhaci.
The banners had hierarchical structure. The minimum unit was niru (or 佐領 zuoling in Chinese; 300 men). The next was jalan (or 參領 canling; 5 niru) and 5 jalan consisted a gūsa (banner). Of course, these were ideal numbers and their actual sizes varied substantially.
Although the banners were instrumental in the Qing Dynasty takeover of China in the 17th century, they began to atrophy in the 18th century, and were militarily useless by the 19th century. The Banners proved unable to either defeat Western powers such as Britain in the Opium Wars nor were they able to defend the dynasty against internal revolts such as the Taiping Rebellion.
By the late 19th century, the Qing Dynasty began training and creating New Army units based on Western training, equipment, and organization. Nevertheless, the banners remained in existence as a military force (albeit a useless one) until the fall of the Qing in 1911.
The Banner system was also applied to Mongolia but was different from the Manchu Eight Banner System. The Qing Dynasty organized the Mongols into banners (qoshuu) except those who belonged to the Mongol Eight Banners.
Each banner had sumun as nominal subdivisions, which also means arrow. Several banners made up a league (chuulghan; 盟 meng). While it restricted the Mongols from crossing banner border, the dynasty protected Mongolia from population pressure from China.