During the reign of the Han Emperor Wudi (140 - 87 BC), Su Wu was sent as an emissary to the ancient Hun court in North China. He had successfully finished his mission and was preparing for backing home when a riot of the upper class of the Huns broke out and his mission was implicated in a plot. He was forbidden to leave the Hun court. 

With an offer of wealth and a high position, the Khan of the Hun tribe tried to persuade Su Wu to yield to his court, but Su Wu still refused to renounce his loyalty to his country. That failed, the Khan had Su Wu put into an open ditch in the cold and snow, without food and water. Su Wu still refused to yield though on the verge of death.

The Khan was even more respected Su Wu for his unswerving patriotism and true grit, yet he was unwilling to let him go back to the Han Dynasty, so he ordered Su Wu banished to the barren lands near the North Sea, which is today's Lake Baikal in Siberia to tend rams. He was not to leave the area, he was told, until the rams bore lambs. It was impossible to return home, but Su Wu endured severe hardship heroically, carrying a bamboo staff with tassels to represent his authority as a Han ambassador while tending the sheep.

Year in and year out, Su Wu's hair and beard had all turned white. Meanwhile, both the old Khan and Emperor Wudi died, the Hun court and the Han Dynasty made peace. A new Han Emperor took the throne and Su Wu was permitted to return home.   

Su Wu, who spent 19 lonely and difficult years in amongst the Huns, was very warmly received by Han officials and the public after his return. For 2,000 years, He has always been eulogized as a hero by later generations.