According to the Records of the Grand Historian, in the first year of Tianhan (200 BC) during the reign of Emperor Wu of Han, Commander-in-Middle Su Wu was dispatched to the Xiongnu and detained for a long time, confined in the frigid region of Beihai (present-day Lake Baikal) for many years. Later, the Han dynasty sent envoys demanding that the Xiongnu release Su Wu, but the Chanyu of the Xiongnu lied, claiming that Su Wu had died. Chang Hui, who accompanied Su Wu on his mission to the Xiongnu, secretly met with the Han envoy, informing him that Su Wu was not dead, and told him to say to the Chanyu: The Han Emperor, while hunting in the Shanglin Park, shot a swan goose, which had a piece of silk cloth tied to its foot, stating that Su Wu was in a large marshland. As a result, the Chanyu of the Xiongnu could no longer falsely claim that Su Wu was dead and had to allow him to return to the Han dynasty. There is also a folk tale from the Tang Dynasty about Xue Pinggui, who was away on a distant campaign, while Wang Baochuan remained faithful, enduring hardship in a cold cave for over a decade. One day, while Wang Baochuan was picking wild vegetables, she heard a swan goose calling repeatedly in the air, and she asked it to deliver a message to her husband Pinggui. However, she found it difficult to locate pen and ink in a hurry. In desperation, she tore off a piece of her silk skirt, bit her fingertip until it bled, wrote a letter stained with blood and tears, pouring out her loyalty to love and longing for family reunion. Due to the circulation of these stories and their transformation into timeless legends, the swan goose has since become a beautiful epithet for a mail carrier.
“Swan Goose Delivering Messages” is an ancient Chinese folk legend. Because the swan goose belongs to a type of migratory bird that observes regular migration cycles, keeps to schedules, gathers in flocks, and demonstrates strong organization, the ancients, with their relatively primitive communication methods, yearned to use this bird, which embodied the virtues of benevolence, righteousness, propriety, wisdom, and faithfulness, to deliver messages and relay information. Historical records show that Su Wu, who was sent by Emperor Wu of Han to the Xiongnu, was held captive by the unpredictable Chanyu for 19 years. When Emperor Zhao ascended the throne, he learned the truth and instructed the newly dispatched Han envoy to tell the Chanyu: “The Han Emperor shot a swan goose from the north while hunting, and there was a letter tied to the goose's leg, stating that Su Wu was tending sheep at Beihai (present-day Lake Baikal).” Seeing his secret revealed, the Chanyu could no longer conceal the truth and released Su Wu back to the Han dynasty. It is from this incident that the term “Swan Goose Delivering Messages” originates.