Ershawan Fort, also known as Haimen Tianxian, is a national historic site located on Ershawan Mountain in Zhongzheng Park. Built using traditional Chinese city gate construction methods, it is imposing and nestled against the mountain. Originally situated on the Ershawan coast, the fort was built around the Daoguang era of the Qing Dynasty (1840 AD). After its destruction, the current site was rebuilt by Liu Mingchuan's troops after the Sino-French War (1885 AD), making it of significant historical value.
Ershawan Fort is a "mountain-embracing fort" among high-ground forts. Unlike ordinary forts, the fort is built on a high, coastal hilltop, while the barracks are designed on a lower-lying area facing away from the sea. Shells from invading enemy ships would only hit the seaward side of the hill or fall over the hill into the valley, making it difficult to hit the barracks. Furthermore, it forms a triangular defensive network with Sheliao and Baimiweng, located at the outer harbor entrance, to defend Keelung's inner and outer harbors.
The existing structures at Ershawan Fortress, such as the city gate, barracks foundations, grand staircase, gun emplacements, sub-walls, and ammunition depots, each have their own unique characteristics. The gun emplacements and sub-walls are constructed using iron and cement, and the fortress area also contains several replicas of ancient cannons. Due to its elevated position and expansive views, visitors can overlook the harbor from the gun emplacements, experiencing the imposing grandeur of the "natural barrier of the sea gate"—a truly magnificent sight. Furthermore, the fortress area is densely wooded with walking trails, making it a great place for forest bathing. Birds and insects inhabit the area, adding a vibrant natural beauty to the historical site visit.