In 1884, a war broke out between the Qing Dynasty and France over Vietnam's sovereignty, and the French attacked Keelung. At that time, the Qing army built a fort on Hongdanshan, and the Qing army used long bamboo poles to stand around the fort. Some bamboo poles raised flags. The French army called it "Fort Bambou".
A place close to the triangular point was once artificially built and flat. This place has a good outlook and is on the ridgeline. It is likely to be the bamboo castle site. And there are many similar sandstone herringbone walls left nearby. It may also be the remains of the "Ten Mile Wall (十里長牆)" built by the Qing army during the Qing-French War, but this requires further investigation and verification.