Yi'an Fortress, Military fortress in Huxi She Ethnic Township, China.

Yi'an Fortress, also called Huxi Fort, is a walled settlement in Chengnei village, Huxi She Ethnic Township, Zhangpu County. Its rammed three-soil walls form a lock-shaped plan 1,200 m around, 6.7 m high and 2.2 m thick, built of large stone blocks. Four gates pierce the wall: Yi'an (south), Yingxi (east), Yuxiu (west) and Chengqing (north); the east, south and west gates carry boat-shaped gate towers, while the north gate has none and was long sealed.

Huang Xingzhen, a Qing official known as a "platform strategist", built Yi'an Fortress in 1687, the 26th year of Kangxi's reign; the Zhangzhou prefectural gazetteer dates the work to 1688 and notes it followed the layout of nearby Zhaojiabao. The name is said to mean "one word settles Taiwan". Huang also founded ancestral halls, charitable fields and a temple school for his lineage.

The name Yi'an is said to mean "one word pacifies Taiwan" or "the pacification of Taiwan," referring to Huang Xingzhen's service as a Qing official. Inside the walls are two Huang ancestral halls: the main one near the south gate and a smaller one near the north gate, built in 1690, with a stone tablet inscribed "以介景福" and a plaque reading "赠公家庙." Couplets there commemorate Huang's career and his support for the clan.

The fortress stands in Chengnei Village, Huxi She Ethnic Township, Zhangpu County, about 1 km from Zhaojiabao. The north gate has no gate tower and was long sealed and once collapsed, so enter by the south gate, named Yi'an, or the east and west gates. A 10-metre-wide moat runs from the south gate to the west gate.

The gate arches have small holes at the top through which defenders could pour hot water or oil on attackers, and also prevent fire attack. The walls carry 365 crenellations, and the loopholes are wide inside and narrow outside so shooters could adjust their angle while staying hidden.