公元四世纪，中国南北分裂。氐族人苻坚建立的前秦统一了北方，势力强盛；南方的东晋则凭借长江天险，保有半壁江山。
In the fourth century AD, China was split between north and south. Former Qin, founded by the Di leader Fu Jian, had unified the north and grown powerful; in the south, Eastern Jin held its half of the empire behind the natural barrier of the Yangtze.
苻坚一心想要统一天下。他召集群臣商议南征，多数人认为东晋上下齐心，又有谢安、谢玄等人才，不宜轻举妄动。苻坚却十分自信，夸口说：“以我军的规模，把马鞭投入江中，也足以截断水流。”
Fu Jian was set on unifying the realm. He summoned his ministers to discuss a southern campaign, and most argued that Eastern Jin was united behind its court and had men of talent such as Xie An and Xie Xuan, so it would be rash to move. Fu Jian was utterly confident, and boasted: “With an army of our size, we could throw our riding whips into the river and stop its flow.”
公元383年，苻坚下令大举南下，号称百万大军，实际兵力也远远超过晋军。东晋以谢石、谢玄等率八万人迎战。
In 383, Fu Jian ordered a great southern campaign, claiming a million men; even in reality his army far outnumbered the Jin. Eastern Jin met him with eighty thousand troops under Xie Shi, Xie Xuan and others.
前秦先锋苻融攻占寿阳。苻坚登上寿阳城楼，远望八公山，看见山上草木摇动，竟以为都是晋军，回头对苻融说：“这也是劲敌啊，怎么能说人少？”
The Former Qin vanguard under Fu Rong took Shouyang. Fu Jian climbed the gate tower and gazed at Mount Bagong. Seeing the trees and grass swaying on the slopes, he took them all for Jin soldiers and said to Fu Rong: “These too are formidable enemies — how can anyone say they are few?”
晋军进驻淝水东岸，与秦军隔水相望。秦军人数虽多，却难以展开。晋将谢玄派人送信，请秦军稍稍后撤，让晋军渡河决战。
The Jin army took up position on the eastern bank of the Fei River, facing the Qin across the water. The Qin had the greater numbers but could not deploy them. The Jin general Xie Xuan sent a message asking the Qin to pull back a little so that the Jin could cross and decide the battle.
秦军将领打算趁晋军渡到一半时发动攻击，便同意后撤。谁知大军一动，阵脚先乱，被俘后归降的晋将朱序又在阵后高喊：“秦军败了！”
The Qin commanders meant to attack while the Jin were halfway across, and so agreed to withdraw. But once the great army began to move, its formation broke down — and Zhu Xu, a captured Jin general now serving the Qin, shouted from the rear: “The Qin army is beaten!”
士兵们信以为真，争相逃命，溃不成军。晋军乘势渡河猛攻，苻融战死，苻坚中箭，单骑逃走。逃亡途中，风吹鹤鸣，秦兵都以为是追兵。
The soldiers believed him and fled for their lives; the army dissolved. The Jin crossed the river and attacked with all their force. Fu Rong was killed, Fu Jian was wounded by an arrow and escaped alone on horseback. As they fled, the wind and the cries of cranes made the Qin troops think the pursuers were upon them.
这一战，前秦元气大伤，北方重新分裂，东晋得以延续。此后，“草木皆兵”和“风声鹤唳”都用来形容人在惊恐中疑神疑鬼、丧失判断。
After this battle Former Qin was crippled, the north broke apart again, and Eastern Jin survived. Ever since, both 草木皆兵 and 风声鹤唳 have described people who, in their terror, suspect every sight and sound and lose all judgement.