Dagu Fort is located in the estuary of the Haihe River in Dagu in Eastern Tanggu District, Tianjing City.

Dagukou was called Jinmen Zhi Ping (Protective Screen for Tianjin) because it served as a coastal defense strategic pass for Northern China and a waterway to Beijing since ancient times. Ramparts and fortifications were built to resist Japanese pirates (14th -16th century) during the Ming Dynasty (1368-1644). In 1858, the eighth year of the reign of the seventh emperor of the Qing Dynasty (1644-1911) Xianfeng, Haikou Liuying (Six Battalions at the Seaport) was set up. Three forts were erected on the northern banks of the Haihe River at Dagukou and two on the southern banks, named respectively with five Chinesecharacters: Wei (powerful), Zhen (guarding), Hai (sea), Men (gate) and Gao (high). Square or round in shape and 10-15 meters in height, all five forts were surrounded by embankment walls full of embrasures encircled by deep trenches. During the reign of Guanxu in 1875, the ninth emperor of the Qing Dynasty by the order of Li Hongzhang (1823-1901) -- the chief minister of the late Qing government -- some forts were added in Dagu, Beitang, etc. By 1885, the 10th year in the reign of Guangxu, there were 52 forts in Dagu. As a result of the humiliating Xinchou Tiaoyue (Treaty in 1901) signed between the Qing government and the 11 countries -- Britain, the United States, Russia, Italy, Japan, France, Spain, Holland and Belgium in 1901 -- in the 27th year of the reign of Guangxu, the Dagu Forts were dismantled. Only the fort on the south bank called Hai (sea) has preserved and has remained comparatively intact. Around the fort, relics of artilleries and shells can still be found.

During the Second Opium War (1856-1860), the Chinese military and the people engaged themselves in the Dagukou Defending Battle against invading colonial armies here. In 1900, the defending Boxers in Tianjin also resisted the invasion of the Eight-Power Allied Forces.