Zhenhai, at the sea mouth of the Yongjiang River, is on the coast of the East Sea. Known as "the Grand Town of the Heaven and the Sea" and "the Gate of Zhejiang," it is an important strategic area of the south-east coast of China to fight against foreign invasions. Undergoing wars against Japanese, French and British invaders in the past over 400 years, Zhenhai has recorded many heroic deeds of the Chinese people and kept rich coast defense relics. Here, as early as the Ming Dynasty, famous generals Lu Tang, Yu Dayou and Qi Jiguang led fierce battles against Japanese pirates on the Yongjiang River and won great victories. Here at Zhenhai in the First Opium War, the national hero Lin Zexu was demoted to Zhenhai to assist the defense. Yuqian, the imperial commissioner and the governor of Zhejiang and Jiangsu, led his army to fight bitter battles against the British enemies and died his heroic death. In the Zhenhai Battle of the Sino-French War in March 1885, Liu Bingzhang (Imperial Inspector of Zhejiang), Ouyang Jianli (Governor of Zhejiang), assisted by Wu Jie and other generals, defeated the French fleet and killed the French chief commander. It is China’s only complete victory in the contemporary history of the sea-coast anti-invasion wars.

On the banks of the Yongjiang River, there are abundant historic coast defense relics. On the top of Zhaobao Mountain, there are the Ming dynasty's forts against Japanese pirates: the Weiyuan Fort, The Moon Fort, the Anyuan Battery, the Table Pavilion in Memory of Wu Jie’s Merit, and tablets set up in the Ming and the Qing Dynasties. Bellow the Mountain, there are the Monument in Memory of the Victory of Zhenhai Battle in the Sino-French War, the Pan Pond in which Yu Qian died, the Great Achievement Temple, the Tablet in Memory of Yu Dayou and galleries. In the Zhenhai City, there are relics as Wu Jie's Residences, Zhenhai Pass and others. About the Golden Cock Mountain on the south bank of the Yongjiang River, there exist the Observatory, the Hongyuan Battery and the Qijiashan Fort. All these relics are the witnesses of the Chinese people's patriotism and their bravery in fighting against foreign invaders and they are also the rich spiritual property of the Chinese people.

The Coast Defense Relics Site is a key unit for national cultural relics preservation. The Memorial Museum of Zhenhai Coast Defense, whose name was inscribed by President Jiang Zeming, is the only museum of the coast-defense history and it is one of the 100 centers for patriotism education of the country.