Treaty of Tientsin
During the Second Opium War, an Anglo-French expedition landed in China and marched towards Peking in order to force the compliance of the Treaty of Tientsin. On 13 August 1860, during the attack on the Taku Forts -- 大沽炮台, in Chinese, or "dàgū pàotái" -- Chinese troops captured two British soldiers and a group of coolies. (Some contemporary accounts record the latter as Sikh soldiers from India, and indeed the poem refers to "dusky Indians")