During that time (in the first century B.C.), the Chinese were often in conflict with the Hsiung-nu border tribes in the north. Su Wu was sent by the Emperor to negotiate with Ch'an Yu, the Hsiung-nu chieftain, who imprisoned him and forced him to work herding sheep.
根據史籍記載，李陵與蘇武都是漢武帝時的武將，蘇武在天漢年間（100B.C.）持節出使匈奴，被單于迫降，不屈，遂扣留北海牧羊。