During the reign of Emperor Wu of the Han Dynasty, in an effort to strengthen ties with southern tribes and find a route to the kingdom of Shendu (modern-day India), the emperor dispatched envoys Wang Ranyu and Bai Shichang to take back roads through the southwest in search of a path to Shendu.
When envoys from the Han Dynasty arrived in the Dian region (modern Yunnan), King Dangqiang of Dian asked, "Compared to our kingdom, which is larger—the Han Dynasty or Dian?" Later, when they reached the Yelang Kingdom, the Yelang king posed the same question. Both rulers, isolated and ignorant of the Han's vastness, genuinely believed their own territories were unmatched in size. The envoys, suppressing a laugh, explained the truth, but the kings remained skeptical.
In the early years of Emperor Wu of Han, while the northern Xiongnu and southern tribes of Ba and Shu constantly rebelled, the emperor sent troops south while stabilizing the north. Tang Meng, summoned for the campaign, proposed in a memorial: "To conquer the south, we must first befriend and pacify the Yelang Kingdom, then use the Zangke River from Yelang as our route south." Emperor Wu adopted Tang Meng's plan, sending him with over ten thousand men and a massive convoy of imperial gifts from Chang'an to Yelang, aiming to transform the kingdom into a Han prefecture.
The ancient Yelang Kingdom was located in what is now western Guizhou, about 20 li northeast of Loushan Pass, and among the sixty-plus tribes of the southwest, it was considered one of the larger states. Surrounded by mountains on all sides, its isolation made travel difficult.
According to historical records, the king of Yelang was named Zhu Duotong, meaning "Bamboo Many Peers." Legend has it that a woman washing clothes by the Dun River suddenly spotted three large bamboo poles floating on the water and heard a baby crying inside. She quickly fished them out, split them open, and found a baby boy, whom she took home to raise. As he grew up, he became both learned and skilled in martial arts, eventually becoming the king of Yelang and taking the surname Zhu, meaning "Bamboo."
When Tang Meng met the King of Yelang, he conveyed the imperial court's wishes, offering the king a marquis title and his son a commandery governorship, along with gifts of fine silks, in exchange for making Yelang a Han commandery. The king, who had never left his own land and knew nothing of the outside world, had always ruled with arrogance. Tang Meng explained, "The Han Empire has thirteen provinces, each with many counties—Yelang's territory is only as large as one Han county." Only then did the king agree to become a Han commandery.
Later, the idiom "Yelang's Arrogance" came to describe those who are isolated, ignorant, and self-important.
Source: *Book of Han*, "Biography of the Southwestern Yi"
Meaning of the Idiom: Later, the Chinese idiom "夜郎自大" came to describe those who are isolated, ignorant, and self-important.