The first fort was built during the reign of the Ming Jiajing Emperor between 1522 and 1527. Its purpose was to protect Tianjin from attack by wokou sea raiders. Later, in 1816, the Qing government built the first two forts on both sides of the Haihe estuary in response to increased concerns about seaborne threats from the West. By 1841, in response to the First Opium War, the defensive system in Dagukou was reinforced into a system of five big forts, 13 earthen batteries, and 13 earthworks. In 1851, Imperial Commissioner Sengge Rinchen carried out a comprehensive renovation of the forts, building 6 large forts: two on the south of the estuary, called "Wēi" (威-Might) and "Zhèn"(震-Thunder, Tremor, Quake), three to the north, "Hǎi"(海-sea), "Mén"(门-gate) "Gāo" (高-high), and the sixth, the "Sh