公元四世纪后期，氐族首领苻坚建立的前秦在谋臣王猛的辅佐下统一北方，国力达到极盛。王猛临终前告诫苻坚：东晋虽弱，却是华夏正统所在，不可轻伐；鲜卑、羌等降部才是心腹之患。苻坚却没有听从。
In the late fourth century, Former Qin, founded by the Di leader Fu Jian, unified the north under the guidance of his minister Wang Meng and reached the height of its power. On his deathbed Wang Meng warned Fu Jian that Eastern Jin, though weak, was the seat of the Chinese legitimate order and must not be lightly attacked, while the surrendered Xianbei and Qiang peoples were the real danger at home. Fu Jian did not listen.
公元383年，苻坚下诏大举南征，征发各族丁壮，号称百万，先锋苻融率二十余万先行。东晋以谢石为征讨大都督，谢玄为前锋，率北府兵八万迎击，兵力悬殊。
In 383 Fu Jian ordered a general southern campaign, conscripting able-bodied men from every people under his rule and claiming a million troops; his vanguard under Fu Rong, more than two hundred thousand strong, went ahead. Eastern Jin made Xie Shi grand commander and Xie Xuan forward commander, and met him with eighty thousand Beifu troops — a vast disparity of force.
苻融攻陷寿阳，梁成率军驻守洛涧。苻坚得知晋军兵少，把大军留在项城，只带八千骑兵赶到寿阳，想一举击溃晋军。
Fu Rong took Shouyang, and Liang Cheng stationed his troops at Luojian. Learning that the Jin army was small, Fu Jian left his main host at Xiangcheng and rode to Shouyang with only eight thousand cavalry, intending to crush the Jin at a single blow.
他登上寿阳城楼，眺望八公山。山上草木随风摇动，他竟疑心漫山遍野都是晋兵，回头对苻融说：“此亦劲敌也，何谓少乎？”此前“投鞭断流”的豪言，此刻已蒙上一层阴影。
He climbed the Shouyang gate tower and gazed at Mount Bagong. The trees and grass stirred in the wind, and he began to suspect that the whole mountainside was covered with Jin soldiers. Turning to Fu Rong he said: “These too are formidable enemies — how can anyone call them few?” The earlier boast that his whips could dam the river was now shadowed by doubt.
晋军方面，刘牢之率北府兵在洛涧大破梁成，斩首万余，士气大振。随后两军在淝水对峙。秦军数量虽多，却无法全部展开，只能沿河列阵。
On the Jin side, Liu Laozhi led the Beifu troops to a crushing victory over Liang Cheng at Luojian, killing more than ten thousand and raising morale enormously. The two armies then faced each other at the Fei River. The Qin had the numbers but could not bring them all into line, and had to array along the bank.
谢玄派人向苻融提议：秦军稍退，让晋军渡河，一决胜负。秦军诸将想趁晋军半渡而击，便答应后撤。然而号令一下，数十万人的阵线立时松动，加上原东晋降将朱序在阵后大呼“秦兵败矣”，军心瞬间崩溃。
Xie Xuan sent word to Fu Rong proposing that the Qin pull back a little and let the Jin cross, so that the issue could be settled. The Qin commanders, intending to strike while the Jin were halfway over, agreed to withdraw. But at the order, the line of hundreds of thousands at once came loose, and Zhu Xu — a former Eastern Jin officer who had gone over to Qin — shouted from the rear, “The Qin army is beaten!” The army’s morale collapsed in an instant.
后撤变成了溃逃。晋军渡河追击，苻融死于乱军之中，苻坚身中流矢，单骑奔逃。逃亡的秦兵听见风声与鹤唳，都以为是追兵，昼夜不敢停歇，冻饿而死者不计其数。
The withdrawal turned into a rout. The Jin crossed in pursuit; Fu Rong died in the confusion, and Fu Jian, struck by a stray arrow, fled alone on horseback. As the Qin soldiers ran, they heard the wind and the cries of cranes and took them for pursuing troops, not daring to rest day or night; countless numbers died of cold and hunger.
淝水一战，前秦土崩瓦解：慕容垂重建燕国，姚苌建立后秦，苻坚本人也在两年后被杀。后世用“草木皆兵”形容人在恐惧中把草木都看成敌兵，用“风声鹤唳”形容疑惧至极、自相惊扰；两个成语的定型与流行，则是后来语言习惯的结果。
At the Fei River, Former Qin fell apart: Murong Chui revived the state of Yan, Yao Chang founded Later Qin, and Fu Jian himself was killed two years later. Later ages used 草木皆兵 — “every bush and tree a soldier” — for seeing plants as enemy troops in one’s fear, and 风声鹤唳 — “wind and crane cries” — for terror so extreme that people startle one another; that the two idioms took their present form and spread widely was the work of later linguistic habit.