Gao Pian and the Broken Dragon Vein: Was Dai La Built to Hold the South or Lock Its Future?

In 866, the Tang general Gao Pian rebuilt Dai La at Tong Binh, in present-day Hanoi. The walls ran for more than 6 km and rose about eight metres. Records describe watchtowers, gates, moats, waterways and roads. The Tang had just retaken Annam from Nanzhao. Gao Pian needed a fortress that could hold soldiers, grain, river traffic and the people around it.

Vietnamese stories gave him a larger crime. They say he flew a paper kite over the country, found its dragon veins, and buried copper and iron to cut off the South's future. The To Lich River, Tan Vien Mountain, Canh Dieu Mountain and other places became stops in that hunt. The rumour says Gao Pian did not merely want to keep Annam for Tang China. He wanted to prevent the land from producing a Vietnamese dynasty.