It means: "Cang Cang" means dark blue, and "boundless" means boundless. The whole poem means that the surrounding sky is boundless, and Yuan Ye is vast and boundless everywhere.
This poem comes from the Song of Chiles in the Southern and Northern Dynasties.
Chile Song
Author: Yuefu poetry anthology
Creation year: Southern and Northern Dynasties?
Chilechuan, at the foot of Yinshan Mountain. The sky is like a vault, and the cage covers four fields.
the sky is grey and wild. Wind blows grass and sees cattle and sheep.
Interpretation: The vast Chile mountains and rivers are just at the foot of Qianliyin Mountain. The sky is like a circular tent, vast and boundless, covering Yuan Ye all around. ? The sky is blue everywhere, and Yuan Ye is boundless. The wind blew and the grass lay low, revealing many cattle and sheep that had been hidden in the grass.
This poem has a clear and generous style unique to the folk songs of the Northern Dynasties, with an open realm, clear language and excellent artistic generalization. Huang Tingjian, a Song Dynasty poet, said that the author of this folk song "hastily used strange words, which covered the truth" (The Inscription and Postscript of the Valley, Volume 7). Because the author is very familiar with the life of grassland herders, he can grasp the main points at once and poke people's hearts.
Extended information:
Lyle Song, selected from Yuefu Poems, is a folk song spread in the Northern Dynasties north of the Yellow River during the Southern and Northern Dynasties, and is generally believed to have been translated from Xianbei into Chinese. Folk songs sing the magnificent and rich scenery of the grassland in the north, and express the lofty sentiments of the Chiles who love their hometown and life.
from the 4th century to the 6th century, most of northern China was under the rule of Xianbei, Xiongnu and other ethnic minorities, and five regimes, namely Northern Wei, Northern Qi and Northern Zhou, were successively established, which was called "Northern Dynasties" in history. The folk songs of the Northern Dynasties are mainly recorded in Chinese after the Northern Wei Dynasty. These songs are bold and vigorous in style, straightforward in lyricism and plain in language, which shows the heroic spirit of the northern nationalities. This folk song "Chile Song" was first recorded in the eighty-sixth volume "Miscellaneous Ballads" in Yuefu Poems compiled by Song Guo Maoqian. It is generally believed that it is a folk song created by the Chiles.
It came into being in the middle and late century. In the history books, the Chile Song was first mentioned by li yanshou in the early years of the Tang Dynasty. In 546 AD, Gao Huan, the founding emperor of the Northern Qi Dynasty, led 1, troops from Jinyang south to attack Yubi, a military town of the Western Wei Dynasty (now southwest of Jishan County in southern Shanxi Province), and he lost 7, troops on his way back to Jinyang. The purpose of writing this "Chile Song" is to boost the morale of the army.
Baidu Encyclopedia-Chilge