At the narrowest bottleneck of the Dali basin, a 650-meter corridor of land pinches tight between the steep slopes of Cangshan's Yunong Peak and the waters of Erhai Lake. Here stands the Longshou Pass, built in 738 AD by Piluoge, the ruler of the Nanzhao Kingdom, to block Tibetan incursions from the north. Along with the southern Longwei Pass, this fortress sealed the valley. In 1253, the defensive line proved so formidable that Kublai Khan’s invading Mongol army abandoned direct assault, choosing instead to scale the grueling heights of the Cangshan Mountains to reach the capital.

The physical remains of this fortress span two square kilometers, defined by massive rammed-earth walls. If you look closely at the exposed earth, you can see the individual layers of construction, each measuring eight to twelve centimeters thick. At the base lies the original Nanzhao foundation. Above it rest bricks stamped with Dali Kingdom inscriptions. At the very top, Ming Dynasty layers bear the distinct marks of a unique engineering technique: builders laid fresh green leaves between each layer of wet earth before ramming it smooth. The leaves decayed centuries ago, leaving thin, dark organic lines fossilized in the dry clay.

Human lives remain bound to these stones. In the fourteenth century, a Ming official named Zhou Neng rebuilt the fortress, stationing soldiers whose descendants still inhabit the surrounding Shangguan Village. At the northwestern corner, a circular-roofed brick bunker from the Republican era features narrow firing slits, showing how the pass maintained its military role into the twentieth century.

In 2009, modern highway construction sliced directly through the monument, carving wide channels through the ancient walls. This destructive act accidentally revealed the complete archaeological sequence of the site. Today, the highway bypasses the ruins, and the breached walls have been repaired using traditional Ming-style techniques. The exposed archaeological profiles remain visible, offering a direct view of thirteen centuries of human labor, conflict, and survival written in the soil.