This sentence came from a poem in Bai Juyi's Song of Everlasting Regret in the Tang Dynasty. The whole sentence was: Three thousand World Crows slaughtered a lone city of ten thousand feet. The meaning of this sentence was that all the crows in the three thousand worlds had been killed, and a lone city towered into the clouds. The emotions expressed in this sentence were sadness, loneliness, and despair. It implied that the poet was in an isolated city surrounded by enemies and surrounded by mountains, unable to receive reinforcements. In this situation, the poet felt lonely and desperate, unable to get help, and might even be killed by the enemy.