山海关

Built in 1381 under the Ming, the pass closes the narrow strip between the Yan Mountains and the Bohai Sea, which gives it its name, 'mountain and sea pass'. Its gate tower carries the inscription 天下第一关, 'the First Pass Under Heaven'. In 1644 the Ming general 吴三桂 opened it to the Qing army, which went on to take Beijing.

The land beyond the pass was 关外 or 关东, and the land inside it 关内. The great migration of the late Qing to the Northeast is still called 闯关东.