During the Western Han Dynasty, Emperor Wu dispatched his minister Su Wu as an envoy to the Western Regions to establish friendly relations with the Xiongnu Chanyu.

However, a Han general who had previously surrendered, King Hou, rebelled, infuriating the Chanyu. Consequently, Su Wu and his entourage were detained.

Su Wu was then confined to a large cellar, where he subsisted by gnawing on snow and swallowing felt, resolutely refusing to capitulate.

He was subsequently forced into slavery by the Xiongnu, herding sheep across the vast grasslands. Nineteen years later, he finally returned to the Han Dynasty, his integrity unbroken.