Hangu Pass, Mountain pass in Henan, China

Hangu Pass is a fortified pass in Lingbao, Sanmenxia, Henan, at the eastern end of the Hangu Valley. Its surviving stone and brick lower wall is pierced by a large arched tunnel; above it a railed terrace holds two grass-covered earthen mounds with arched openings and tiled roof caps, with yellow flags along the railing.

The Qin state built fortifications at the pass in 361 BC to mark its eastern border and create a defensive position against rival territories. The Han dynasty later expanded the site, adding more roads and platforms that archaeologists uncovered between 2012 and 2013.

The name comes from the road running through a deep loess ravine, "deep and dangerous like a box" (函, han). The pass is a Daoist holy site: tradition holds that Laozi wrote the 5,000-character Daodejing here at the request of the keeper Yin Xi. On 19 May 2009 Lingbao held a reading of the Daodejing by a thousand people at the Taichu Palace, and on 27 March 2021, the 2,592nd anniversary of Laozi's legendary birth, the city ran a Daodejing culture week.

Regular buses run from Luoyang to Xin'an, where the archaeological site and museum park are located. Guided tours in several languages are available and help explain the defensive systems and excavation findings.

Excavations have uncovered over 3,000 square meters of ancient structures, including well-preserved road sections that show how travelers and troops moved through the pass. Some stone slabs still carry visible wheel ruts from the Han period.